fix libffi testsuite on Darwin

[Geoffrey Keating]

Using -lgcc_s bad.  Using -shared-libgcc better.  Having a
comment to explain what's going on, *much* better.

Tested by running the libffi testsuite.  No failures!

-- 
- Geoffrey Keating <geoffk@apple.com>

===File ~/patches/gcc-darwin-minversionlibgccffitests.patch===
2005-09-30  Geoffrey Keating  <geoffk@apple.com>

	* testsuite/lib/libffi-dg.exp (libffi_target_compile): For
	darwin, use -shared-libgcc not -lgcc_s, and explain why.

Index: testsuite/lib/libffi-dg.exp
===================================================================
RCS file: /cvs/gcc/gcc/libffi/testsuite/lib/libffi-dg.exp,v
retrieving revision 1.13
diff -u -p -u -p -r1.13 libffi-dg.exp
--- testsuite/lib/libffi-dg.exp	20 Apr 2005 10:59:26 -0000	1.13
+++ testsuite/lib/libffi-dg.exp	1 Oct 2005 06:03:46 -0000
@@ -187,8 +187,13 @@ proc libffi_target_compile { source dest
     lappend options "additional_flags=-I${libffi_include} -I${srcdir}/../include  -I${libffi_include}/.."
     lappend options "additional_flags=${libffi_link_flags}"
 
-    if { [string match "powerpc-*-darwin*" $target_triplet] } {
-	lappend options "libs= -lgcc_s"
+    # If you're building the compiler with --prefix set to a place
+    # where it's not yet installed, then the linker won't be able to
+    # find the libgcc used by libffi.dylib.  We could pass the
+    # -dylib_file option, but that's complicated, and it's much easier
+    # to just make the linker find libgcc using -L options.
+    if { [string match "*-*-darwin*" $target_triplet] } {
+	lappend options "libs= -shared-libgcc"
     }
 
     lappend options "libs= -lffi"
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