[gcc] Allow GCC insert .cfi_startproc and .cfi_endproc.

NaCl GAS supports these assembler directives. Though on Mac buildbots this
capability is not recognized due to the lack of readelf installed. Supporting
these directives is essential to have correct backtraces listed with valgrind.

BUG: http://code.google.com/p/nativeclient/issues/detail?id=663

Review URL: http://codereview.chromium.org/2805058
diff --git a/gcc/config/i386/nacl.h b/gcc/config/i386/nacl.h
index 2a8bb97..4b3d734 100644
--- a/gcc/config/i386/nacl.h
+++ b/gcc/config/i386/nacl.h
@@ -240,6 +240,11 @@
 #undef HAVE_AS_GOTOFF_IN_DATA
 #define HAVE_AS_GOTOFF_IN_DATA 1
 
+/* Configure script incorrectly detects HAVE_GAS_CFI_DIRECTIVE when readelf is
+ * not found in PATH. */
+#undef HAVE_GAS_CFI_DIRECTIVE
+#define HAVE_GAS_CFI_DIRECTIVE 1
+
 /* NaCl reserves R15 and makes RBP special in x86-64 mode */
 #undef FIXED_REGISTERS
 #define FIXED_REGISTERS						\