RISC-V: Add configure option: --with-multilib-generator to flexible config multi-lib settings.

 - Able to configure complex multi-lib rule in configure time, without modify
   any in-tree source.

 - I was consider to implmenet this into `--with-multilib-list` option,
   but I am not sure who will using that with riscv*-*-elf*, so I decide to
   using another option name for that.

 - --with-multilib-generator will pass arguments to multilib-generator, and
   then using the generated multi-lib config file to build the toolchain.

   e.g. Build riscv gcc, default arch/abi is rv64gc/lp64, and build multilib
       for rv32imafd/ilp32 and rv32i/ilp32; rv32ic/ilp32 will reuse
       rv32i/ilp32.
    $ <GCC-SRC>/configure \
       --target=riscv64-elf \
       --with-arch=rv64gc --with-abi=lp64 \
       --with-multilib-generator=rv32i-ilp32--c;rv32imafd-ilp32--

V3 Changes:

 - Rename --with-multilib-config to --with-multilib-generator
 - Check --with-multilib-generator and --with-multilib-list can't be used at
   same time.

V2 Changes:

 - Fix --with-multilib-config hanling on non riscv*-*-elf* triple.

gcc/ChangeLog:

	* config.gcc (riscv*-*-*): Handle --with-multilib-generator.
	* configure: Regen.
	* configure.ac: Add --with-multilib-generator.
	* config/riscv/multilib-generator: Exit when parsing arch string error.
	* config/riscv/t-withmultilib-generator: New.
	* doc/install.texi: Document --with-multilib-generator.

gcc/config.gcc

@@ -2450,11 +2450,13 @@ riscv*-*-elf* | riscv*-*-rtems*)
 	  tmake_file="${tmake_file} riscv/t-rtems"
 	  ;;
 	*)
+	  if test "x${with_multilib_generator}" == xdefault; then
 		  case "x${enable_multilib}" in
 		  xno) ;;
 		  xyes) tmake_file="${tmake_file} riscv/t-elf-multilib" ;;
 		  *) echo "Unknown value for enable_multilib"; exit 1
 		  esac
+	  fi
 	esac
 	tmake_file="${tmake_file} riscv/t-riscv"
 	gnu_ld=yes
@@ -4581,6 +4583,30 @@ case "${target}" in
 			exit 1
 			;;
 		esac
+		# Handle --with-multilib-generator.
+		if test "x${with_multilib_generator}" != xdefault; then
+			if test "x${with_multilib_list}" != xdefault; then
+				echo "--with-multilib-list= can't used with --with-multilib-generator= at same time" 1>&2
+				exit 1
+			fi
+			case "${target}" in
+			riscv*-*-elf*)
+				if ${srcdir}/config/riscv/multilib-generator \
+					`echo ${with_multilib_generator} | sed 's/;/ /g'`\
+					> t-multilib-config;
+				then
+					tmake_file="${tmake_file} riscv/t-withmultilib-generator"
+				else
+					echo "invalid option for --with-multilib-generator" 1>&2
+					exit 1
+				fi
+				;;
+			*)
+				echo "--with-multilib-generator= is not supported for ${target}, only supported for riscv*-*-elf*" 1>&2
+				exit 1
+				;;
+			esac
+		fi
 
 		# Handle --with-multilib-list.
 		if test "x${with_multilib_list}" != xdefault; then

gcc/config/riscv/multilib-generator

@@ -194,7 +194,14 @@ def expand_combination(ext):
   return ext
 
 for cfg in sys.argv[1:]:
+  try:
     (arch, abi, extra, ext) = cfg.split('-')
+  except:
+    print ("Invalid configure string %s, <arch>-<abi>-<extra>-<extensions>\n"
+           "<extra> and <extensions> can be empty, "
+           "e.g. rv32imafd-ilp32--" % cfg)
+    sys.exit(1)
+
   arch = arch_canonicalize (arch)
   arches[arch] = 1
   abis[abi] = 1

gcc/config/riscv/t-withmultilib-generator

+# t-multilib-config will generated in build folder by configure script.
+include t-multilib-config

gcc/configure

@@ -969,6 +969,7 @@ with_documentation_root_url
 with_changes_root_url
 enable_languages
 with_multilib_list
+with_multilib_generator
 with_zstd
 with_zstd_include
 with_zstd_lib
@@ -1806,6 +1807,8 @@ Optional Packages:
   --with-changes-root-url=URL
                           Root for GCC changes URLs
   --with-multilib-list    select multilibs (AArch64, SH and x86-64 only)
+  --with-multilib-generator
+                          Multi-libs configuration string (RISC-V only)
   --with-zstd=PATH        specify prefix directory for installed zstd library.
                           Equivalent to --with-zstd-include=PATH/include plus
                           --with-zstd-lib=PATH/lib
@@ -8006,6 +8009,15 @@ else
 fi
 
 
+
+# Check whether --with-multilib-generator was given.
+if test "${with_multilib_generator+set}" = set; then :
+  withval=$with_multilib_generator; :
+else
+  with_multilib_generator=default
+fi
+
+
 # -------------------------
 # Checks for other programs
 # -------------------------
@@ -19020,7 +19032,7 @@ else
   lt_dlunknown=0; lt_dlno_uscore=1; lt_dlneed_uscore=2
   lt_status=$lt_dlunknown
   cat > conftest.$ac_ext <<_LT_EOF
-#line 19023 "configure"
+#line 19035 "configure"
 #include "confdefs.h"
 
 #if HAVE_DLFCN_H
@@ -19126,7 +19138,7 @@ else
   lt_dlunknown=0; lt_dlno_uscore=1; lt_dlneed_uscore=2
   lt_status=$lt_dlunknown
   cat > conftest.$ac_ext <<_LT_EOF
-#line 19129 "configure"
+#line 19141 "configure"
 #include "confdefs.h"
 
 #if HAVE_DLFCN_H

gcc/configure.ac

@@ -1110,6 +1110,11 @@ AC_ARG_WITH(multilib-list,
 :,
 with_multilib_list=default)
 
+AC_ARG_WITH(multilib-generator,
+[AS_HELP_STRING([--with-multilib-generator], [Multi-libs configuration string (RISC-V only)])],
+:,
+with_multilib_generator=default)
+
 # -------------------------
 # Checks for other programs
 # -------------------------

gcc/doc/install.texi

@@ -1250,6 +1250,37 @@ If @option{--with-multilib-list} is not given, then only 32-bit and
 64-bit run-time libraries will be enabled.
 @end table
 
+@item --with-multilib-generator=@var{config}
+Specify what multilibs to build.  @var{config} is a semicolon separated list of
+values, possibly consisting of a single value.  Currently only implemented
+for riscv*-*-elf*.  The accepted values and meanings are given below.
+
+
+Every config is constructed with four components: architecture string, ABI,
+reuse rule with architecture string and reuse rule with sub-extension.
+
+Example 1: Add multi-lib suppport for rv32i with ilp32.
+@smallexample
+rv32i-ilp32--
+@end smallexample
+
+Example 2: Add multi-lib suppport for rv32i with ilp32 and rv32imafd with ilp32.
+@smallexample
+rv32i-ilp32--;rv32imafd-ilp32--
+@end smallexample
+
+Example 3: Add multi-lib suppport for rv32i with ilp32; rv32im with ilp32 and
+rv32ic with ilp32 will reuse this multi-lib set.
+@smallexample
+rv32i-ilp32-rv32im-c
+@end smallexample
+
+Example 4: Add multi-lib suppport for rv64ima with lp64; rv64imaf with lp64,
+rv64imac with lp64 and rv64imafc with lp64 will reuse this multi-lib set.
+@smallexample
+rv64ima-lp64--f,c,fc
+@end smallexample
+
 @item --with-endian=@var{endians}
 Specify what endians to use.
 Currently only implemented for sh*-*-*.