buildgcc: Fix function prototype in GCC

With some newer versions of GCC (experienced with GCC 6.2.1 on Arch-
Linux) the first stage of a boostrapping fails due to a mismatching
function prototype. Also add a missing `static` to the signature.

Change-Id: Ia927036ccd725550f1191890515578bc80c74f80
Signed-off-by: Nico Huber <nico.h@gmx.de>
Reviewed-on: https://review.coreboot.org/17704
Tested-by: build bot (Jenkins)
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>

util/crossgcc/patches/gcc-5.3.0_libc_name_p.patch

@@ -0,0 +1,24 @@
+diff -urp gcc-5.3.0.bak/gcc/cp/cfns.h gcc-5.3.0/gcc/cp/cfns.h
+--- gcc-5.3.0.bak/gcc/cp/cfns.h	2015-01-05 13:33:28.000000000 +0100
++++ gcc-5.3.0/gcc/cp/cfns.h	2016-12-04 01:33:47.568537831 +0100
+@@ -51,8 +51,12 @@ along with GCC; see the file COPYING3.
+ __inline
+ #endif
+ static unsigned int hash (const char *, unsigned int);
++static
+ #ifdef __GNUC__
+ __inline
++#ifdef __GNUC_STDC_INLINE__
++__attribute__ ((__gnu_inline__))
++#endif
+ #endif
+ const char * libc_name_p (const char *, unsigned int);
+ /* maximum key range = 391, duplicates = 0 */
+@@ -122,6 +126,7 @@ hash (register const char *str, register
+   return hval + asso_values[(unsigned char)str[len - 1]];
+ }
+ 
++static
+ #ifdef __GNUC__
+ __inline
+ #ifdef __GNUC_STDC_INLINE__