Consistently use -std=gnu99 for gcc as well as clang.

This matters for C files that are also built for Windows. Previously they'd
be compiled with -std=gnu99 for the host but [effectively] -std=gnu89 for
Windows.

Bug: http://b/32019064
Test: builds, and can build libcrypto_utils without a manual -std= line
Change-Id: I9c5cc7832220b5c3d6a007ff10d076e26fd8c75d
diff --git a/cc/makevars.go b/cc/makevars.go
index ea32121..3dd0f74 100644
--- a/cc/makevars.go
+++ b/cc/makevars.go
@@ -113,7 +113,9 @@
 		toolchain.ToolchainCflags(),
 		productExtraCflags,
 	}, " "))
-	ctx.Strict(makePrefix+"GLOBAL_CONLYFLAGS", "")
+	ctx.Strict(makePrefix+"GLOBAL_CONLYFLAGS", strings.Join([]string{
+		"${config.CommonGlobalConlyflags}",
+	}, " "))
 	ctx.Strict(makePrefix+"GLOBAL_CPPFLAGS", strings.Join([]string{
 		"${config.CommonGlobalCppflags}",
 		toolchain.Cppflags(),
@@ -161,7 +163,6 @@
 			clangExtras,
 			productExtraCflags,
 		}, " "))
-		ctx.Strict(clangPrefix+"GLOBAL_CONLYFLAGS", "${config.ClangExtraConlyflags}")
 		ctx.Strict(clangPrefix+"GLOBAL_CPPFLAGS", strings.Join([]string{
 			"${config.CommonClangGlobalCppflags}",
 			toolchain.ClangCppflags(),