configure.in: Detect mmap.

        * configure.in: Detect mmap.  Add --with-gc=foo to select
        garbage collector; default to page if mmap available.
        * Makefile.in (GGC): Substitute.

From-SVN: r29853

gcc/ChangeLog

+Thu Oct  7 01:13:15 1999  Richard Henderson  <rth@cygnus.com>
+
+	* configure.in: Detect mmap.  Add --with-gc=foo to select
+	garbage collector; default to page if mmap available.
+	* Makefile.in (GGC): Substitute.
+
 Wed Oct  6 23:56:30 1999  Richard Henderson  <rth@cygnus.com>
 
 	* c-decl.c (ggc_p): Enable.

gcc/Makefile.in

@@ -308,7 +308,7 @@ CLIB=
 OBSTACK=obstack.o
 
 # The GC method to be used on this system.
-GGC=ggc-simple.o
+GGC=@GGC@.o
 
 # If a supplementary library is being used for the GC.
 GGC_LIB=

gcc/configure.in

@@ -385,6 +385,7 @@ case "${host}" in
   ;;
 esac
 AC_FUNC_VFORK
+AC_FUNC_MMAP
 
 GCC_NEED_DECLARATIONS(bcopy bzero bcmp \
 	index rindex getenv atol sbrk abort atof strerror getcwd getwd \
@@ -4430,6 +4431,26 @@ if test $thread_file != single; then
 fi
 AC_SUBST(gthread_flags)
 
+# Find out what GC implementation we want, or may, use.
+AC_ARG_WITH(gc,
+[  --with-gc={simple,page} Choose the garbage collection mechanism to use
+                           with the compiler.],
+[case "$withval" in
+  simple | page)
+    GGC=ggc-$withval
+    ;;
+  *)
+    AC_MSG_ERROR([$withval is an invalid option to --with-gc])
+    ;;
+esac],
+[if test $ac_cv_func_mmap_fixed_mapped = yes; then
+  GGC=ggc-page
+else
+  GGC=ggc-simple
+fi])
+AC_SUBST(GGC)
+echo "Using $GGC for garbage collection."
+
 # Make empty files to contain the specs and options for each language.
 # Then add #include lines to for a compiler that has specs and/or options.