[PATCH] xen: Don't use -nostdinc flags with CLANG

[Julien Grall <julien.grall@linaro.org>]

Commit 06a9c7e "xen: move -nostdinc into common Rules.mk." breaks
compilation with clang:

In file included from sched_sedf.c:8:
In file included from /home/julieng/works/xen/xen/include/xen/lib.h:5:
/home/julieng/works/xen/xen/include/xen/stdarg.h:20:12: error: 'stdarg.h' file
not found with <angled> include; use "quotes" instead
           ^~~~~~~~~~
           "stdarg.h"
In file included from sched_sedf.c:8:
/home/julieng/works/xen/xen/include/xen/lib.h:101:63: error: unknown type name 'va_list'
extern int vsnprintf(char *buf, size_t size, const char *fmt, va_list args)
                                                              ^
/home/julieng/works/xen/xen/include/xen/lib.h:105:64: error: unknown type name 'va_list'
extern int vscnprintf(char *buf, size_t size, const char *fmt, va_list args)

I have the same errors on different version of clang:
    - clang 3.0 on debian wheezy
    - clang 3.3 on Fedora 20
    - clang 3.5 build from trunk

Removing -nostdinc fix the build on clang.

Signed-off-by: Julien Grall <julien.grall@linaro.org>
---
 xen/Rules.mk | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/xen/Rules.mk b/xen/Rules.mk
index df1428f..ed9b8d0 100644
--- a/xen/Rules.mk
+++ b/xen/Rules.mk
@@ -46,7 +46,8 @@ CFLAGS += -Werror -Wredundant-decls -Wno-pointer-arith
 CFLAGS += -pipe -g -D__XEN__ -include $(BASEDIR)/include/xen/config.h
 # Solaris puts stdarg.h &c in the system include directory.
 ifneq ($(XEN_OS),SunOS)
-CFLAGS += -nostdinc -iwithprefix include
+CFLAGS-y        += -iwithprefix include
+CFLAGS-$(gcc)   += -nostdinc
 endif
 
 CFLAGS-$(XSM_ENABLE)    += -DXSM_ENABLE
-- 
1.8.5.3