cygwin: fix errors with GCC 5

GCC 5 switched from C89 to C11 by default. This implies a change from
GNU to C99 inline by default, which have very different meanings of
extern inline vs. static inline:

https://gcc.gnu.org/onlinedocs/gcc/Inline.html

Marking these as gnu_inline retains the previous behaviour.

	winsup/cygwin/
	* exceptions.cc (exception::handle): Change debugging to int to fix
	an always-true boolean comparison warning.
	* include/cygwin/config.h (__getreent): Mark gnu_inline.
	* winbase.h (ilockcmpexch, ilockcmpexch64): Ditto.

Signed-off-by: Yaakov Selkowitz <yselkowi@redhat.com>

winsup/cygwin/include/cygwin/config.h

@@ -43,6 +43,7 @@ extern "C" {
 #else
 #include "../tlsoffsets.h"
 #endif
+__attribute__((gnu_inline))
 extern inline struct _reent *__getreent (void)
 {
   register char *ret;