libgo patch committed: Don't use == for string equality in C code

[Ian Lance Taylor via Gcc-patches]

This patch to libgo avoids using == for string equality in C code.
This is a backport of https://golang.org/cl/300993.  This is for GCC
PR 99553.  Bootstrapped and ran gotools testsuite on
x86_64-pc-linux-gnu.  Committed to mainline.

Ian

eb7eb29c37b1326bd4c8af7e5c35439a5d4521d4
diff --git a/gcc/go/gofrontend/MERGE b/gcc/go/gofrontend/MERGE
index 58c881a7872..e5756c6662c 100644
--- a/gcc/go/gofrontend/MERGE
+++ b/gcc/go/gofrontend/MERGE
@@ -1,4 +1,4 @@
-bf35249a7c752836741b1cab43a312f87916fcb0
+2f281eb24ef256a2d3bb9fc1a7ef964d82b40182
 
 The first line of this file holds the git revision number of the last
 merge done from the gofrontend repository.
diff --git a/libgo/misc/cgo/testcarchive/testdata/main_unix.c 
b/libgo/misc/cgo/testcarchive/testdata/main_unix.c
index b23ac1c2428..bd00f9d2339 100644
--- a/libgo/misc/cgo/testcarchive/testdata/main_unix.c
+++ b/libgo/misc/cgo/testcarchive/testdata/main_unix.c
@@ -36,7 +36,7 @@ int install_handler() {
                return 2;
        }
        // gccgo does not set SA_ONSTACK for SIGSEGV.
-       if (getenv("GCCGO") == "" && (osa.sa_flags&SA_ONSTACK) == 0) {
+       if (getenv("GCCGO") == NULL && (osa.sa_flags&SA_ONSTACK) == 0) {
                fprintf(stderr, "Go runtime did not install signal handler\n");
                return 2;
        }