[newlib-cygwin] cygwin: workaround GCC 6 changes

[Yaakov Selkowitz <yselkowitz at sourceware dot org>]

https://sourceware.org/git/gitweb.cgi?p=newlib-cygwin.git;h=05cfd1aed8b262e82f62acc2de2858d2d2b6679c

commit 05cfd1aed8b262e82f62acc2de2858d2d2b6679c
Author: Yaakov Selkowitz <yselkowi@redhat.com>
Date:   Tue Sep 12 14:30:34 2017 -0500

    cygwin: workaround GCC 6 changes
    
    GCC 6 includes a number of new warnings which cause Cygwin to either not
    compile, or not work properly even if said warnings are ignored:
    
    https://cygwin.com/ml/cygwin-developers/2017-09/msg00000.html
    https://gcc.gnu.org/gcc-6/porting_to.html
    
    For now, we use the flags necessary to revert to GCC 5 behaviour until we
    can fix the code properly.
    
    Signed-off-by: Yaakov Selkowitz <yselkowi@redhat.com>

Diff:
---
 winsup/cygwin/Makefile.in | 4 ++--
 winsup/cygwin/crt0.c      | 2 ++
 winsup/cygwin/init.cc     | 2 ++
 3 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/winsup/cygwin/Makefile.in b/winsup/cygwin/Makefile.in
index 10e6b1f..98727c0 100644
--- a/winsup/cygwin/Makefile.in
+++ b/winsup/cygwin/Makefile.in
@@ -73,11 +73,11 @@ CRT0:=$(cygwin_build)/crt0.o
 #
 MT_SAFE:=@MT_SAFE@
 CCEXTRA=
-COMMON_CFLAGS=-MMD ${$(*F)_CFLAGS} -Werror -fmerge-constants -ftracer $(CCEXTRA)
+COMMON_CFLAGS=-MMD ${$(*F)_CFLAGS} -Werror -fno-delete-null-pointer-checks -fmerge-constants -ftracer $(CCEXTRA)
 ifeq ($(target_cpu),x86_64)
 COMMON_CFLAGS+=-mcmodel=small
 endif
-COMPILE.cc+=${COMMON_CFLAGS}
+COMPILE.cc+=${COMMON_CFLAGS} -std=gnu++98
 COMPILE.c+=${COMMON_CFLAGS}
 
 AR:=@AR@
diff --git a/winsup/cygwin/crt0.c b/winsup/cygwin/crt0.c
index f0103b4..271f5b9 100644
--- a/winsup/cygwin/crt0.c
+++ b/winsup/cygwin/crt0.c
@@ -20,7 +20,9 @@ void
 mainCRTStartup ()
 {
 #ifdef __i386__
+#pragma GCC diagnostic ignored "-Wframe-address"
   (void)__builtin_return_address(1);
+#pragma GCC diagnostic pop
   asm volatile ("andl $-16,%%esp" ::: "%esp");
 #endif
 
diff --git a/winsup/cygwin/init.cc b/winsup/cygwin/init.cc
index 5b84b1c..2d4299e 100644
--- a/winsup/cygwin/init.cc
+++ b/winsup/cygwin/init.cc
@@ -23,7 +23,9 @@ static void WINAPI
 threadfunc_fe (VOID *arg)
 {
 #ifndef __x86_64__
+#pragma GCC diagnostic ignored "-Wframe-address"
   (void)__builtin_return_address(1);
+#pragma GCC diagnostic pop
   asm volatile ("andl $-16,%%esp" ::: "%esp");
 #endif
   _cygtls::call ((DWORD (*)  (void *, void *)) TlsGetValue (_my_oldfunc), arg);