libgo patch committed: Pass -funwind-tables when compiling C code

[Ian Lance Taylor]

This patch to the go tool in libgo changes it to use -funwind-tables
when compiling C code to support the cgo tool.  Using -funwind-tables
is necessary to permit Go code to correctly throw a panic through C
code.  This hasn't been necessary in the past as -funwind-tables is
the default on x86.  However, it is not the default for PPC AIX, among
other systems.  Bootstrapped and ran Go testsuite on
x86_64-pc-linux-gnu.  Committed to mainline.

Ian

Index: gcc/go/gofrontend/MERGE
===================================================================
--- gcc/go/gofrontend/MERGE     (revision 251133)
+++ gcc/go/gofrontend/MERGE     (working copy)
@@ -1,4 +1,4 @@
-152164a7249ecc5c2bfd4a091450dc7c2855f609
+9ff49c64ea6dbb5e08d1fa859b99b06049413279
 
 The first line of this file holds the git revision number of the last
 merge done from the gofrontend repository.
Index: libgo/go/cmd/go/build.go
===================================================================
--- libgo/go/cmd/go/build.go    (revision 250873)
+++ libgo/go/cmd/go/build.go    (working copy)
@@ -3268,6 +3268,12 @@ func (b *builder) ccompilerCmd(envvar, d
                a = append(a, "-fno-common")
        }
 
+       // gccgo uses the language-independent exception mechanism to
+       // handle panics, so it always needs unwind tables.
+       if _, ok := buildToolchain.(gccgoToolchain); ok {
+               a = append(a, "-funwind-tables")
+       }
+
        return a
 }