libatomic/test: Fix compilation for build sysroot

Fix a problem with the libatomic testsuite using a method to determine
the compiler to use resulting in the tool being different from one the
library has been built with, and causing a catastrophic failure from the
lack of a suitable `--sysroot=' option where the `--with-build-sysroot='
configuration option has been used to build the compiler resulting in
the inability to link executables.

Address this problem by providing a DejaGNU configuration file defining
the compiler to use, via the GCC_UNDER_TEST TCL variable, set from $CC
by autoconf, which will have all the required options set for the target
compiler to build executables in the environment configured, removing
failures like:

.../bin/riscv64-linux-gnu-ld: cannot find crt1.o: No such file or directory
.../bin/riscv64-linux-gnu-ld: cannot find -lm
collect2: error: ld returned 1 exit status
compiler exited with status 1
FAIL: libatomic.c/atomic-compare-exchange-1.c (test for excess errors)
Excess errors:
.../bin/riscv64-linux-gnu-ld: cannot find crt1.o: No such file or directory
.../bin/riscv64-linux-gnu-ld: cannot find -lm

UNRESOLVED: libatomic.c/atomic-compare-exchange-1.c compilation failed to produce executable

and bringing overall test results for the `riscv64-linux-gnu' target
(here with the `x86_64-linux-gnu' host and RISC-V QEMU in the Linux user
emulation mode as the target board) from:

		=== libatomic Summary ===

# of unexpected failures	27
# of unresolved testcases	27

to:

		=== libatomic Summary ===

# of expected passes		54

	libatomic/
	* configure.ac: Add testsuite/libatomic-site-extra.exp to output
	files.
	* configure: Regenerate.
	* libatomic/testsuite/libatomic-site-extra.exp.in: New file.
	* testsuite/Makefile.am (EXTRA_DEJAGNU_SITE_CONFIG): New
	variable.
	* testsuite/Makefile.in: Regenerate.

libatomic/ChangeLog

+2020-04-06  Maciej W. Rozycki  <macro@wdc.com>
+
+	* configure.ac: Add testsuite/libatomic-site-extra.exp to output
+	files.
+	* configure: Regenerate.
+	* libatomic/testsuite/libatomic-site-extra.exp.in: New file.
+	* testsuite/Makefile.am (EXTRA_DEJAGNU_SITE_CONFIG): New
+	variable.
+	* testsuite/Makefile.in: Regenerate.
+
 2020-02-22  Jakub Jelinek  <jakub@redhat.com>
 
 	PR other/55930

libatomic/configure

@@ -15728,6 +15728,8 @@ fi
 
 ac_config_files="$ac_config_files Makefile testsuite/Makefile"
 
+ac_config_files="$ac_config_files testsuite/libatomic-site-extra.exp"
+
 cat >confcache <<\_ACEOF
 # This file is a shell script that caches the results of configure
 # tests run on this system so they can be shared between configure
@@ -16799,6 +16801,7 @@ do
     "gstdint.h") CONFIG_COMMANDS="$CONFIG_COMMANDS gstdint.h" ;;
     "Makefile") CONFIG_FILES="$CONFIG_FILES Makefile" ;;
     "testsuite/Makefile") CONFIG_FILES="$CONFIG_FILES testsuite/Makefile" ;;
+    "testsuite/libatomic-site-extra.exp") CONFIG_FILES="$CONFIG_FILES testsuite/libatomic-site-extra.exp" ;;
 
   *) as_fn_error $? "invalid argument: \`$ac_config_target'" "$LINENO" 5;;
   esac

libatomic/configure.ac

@@ -288,4 +288,5 @@ else
 fi
 
 AC_CONFIG_FILES(Makefile testsuite/Makefile)
+AC_CONFIG_FILES(testsuite/libatomic-site-extra.exp)
 AC_OUTPUT

libatomic/testsuite/Makefile.am

@@ -11,3 +11,5 @@ EXPECT = $(shell if test -f $(top_builddir)/../expect/expect; then \
 _RUNTEST = $(shell if test -f $(top_srcdir)/../dejagnu/runtest; then \
 	     echo $(top_srcdir)/../dejagnu/runtest; else echo runtest; fi)
 RUNTEST = $(_RUNTEST) $(AM_RUNTESTFLAGS)
+
+EXTRA_DEJAGNU_SITE_CONFIG = libatomic-site-extra.exp

libatomic/testsuite/Makefile.in

@@ -109,7 +109,7 @@ am__configure_deps = $(am__aclocal_m4_deps) $(CONFIGURE_DEPENDENCIES) \
 DIST_COMMON = $(srcdir)/Makefile.am
 mkinstalldirs = $(SHELL) $(top_srcdir)/../mkinstalldirs
 CONFIG_HEADER = $(top_builddir)/auto-config.h
-CONFIG_CLEAN_FILES =
+CONFIG_CLEAN_FILES = libatomic-site-extra.exp
 CONFIG_CLEAN_VPATH_FILES =
 AM_V_P = $(am__v_P_@AM_V@)
 am__v_P_ = $(am__v_P_@AM_DEFAULT_V@)
@@ -278,6 +278,7 @@ _RUNTEST = $(shell if test -f $(top_srcdir)/../dejagnu/runtest; then \
 	     echo $(top_srcdir)/../dejagnu/runtest; else echo runtest; fi)
 
 RUNTEST = $(_RUNTEST) $(AM_RUNTESTFLAGS)
+EXTRA_DEJAGNU_SITE_CONFIG = libatomic-site-extra.exp
 all: all-am
 
 .SUFFIXES:
@@ -310,6 +311,8 @@ $(top_srcdir)/configure: @MAINTAINER_MODE_TRUE@ $(am__configure_deps)
 $(ACLOCAL_M4): @MAINTAINER_MODE_TRUE@ $(am__aclocal_m4_deps)
 	cd $(top_builddir) && $(MAKE) $(AM_MAKEFLAGS) am--refresh
 $(am__aclocal_m4_deps):
+libatomic-site-extra.exp: $(top_builddir)/config.status $(srcdir)/libatomic-site-extra.exp.in
+	cd $(top_builddir) && $(SHELL) ./config.status $(subdir)/$@
 
 mostlyclean-libtool:
 	-rm -f *.lo

libatomic/testsuite/libatomic-site-extra.exp.in

+set GCC_UNDER_TEST {@CC@}