Modify configure to determine return value of strerror_r.

On glibc and Android's bionic, strerror_r returns char* when
_GNU_SOURCE is defined.

Add a configure check for this rather than assume glibc is the
only libc that behaves this way.

configure.ac

@@ -2072,6 +2072,25 @@ if test "x${je_cv_pthread_mutex_adaptive_np}" = "xyes" ; then
   AC_DEFINE([JEMALLOC_HAVE_PTHREAD_MUTEX_ADAPTIVE_NP], [ ])
 fi
 
+JE_CFLAGS_SAVE()
+JE_CFLAGS_ADD([-D_GNU_SOURCE])
+JE_CFLAGS_ADD([-Werror])
+JE_CFLAGS_ADD([-herror_on_warning])
+JE_COMPILABLE([strerror_r returns char with gnu source], [
+#include <errno.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+], [
+  char *buffer = (char *) malloc(100);
+  char *error = strerror_r(EINVAL, buffer, 100);
+  printf("%s\n", error);
+], [je_cv_strerror_r_returns_char_with_gnu_source])
+JE_CFLAGS_RESTORE()
+if test "x${je_cv_strerror_r_returns_char_with_gnu_source}" = "xyes" ; then
+  AC_DEFINE([JEMALLOC_STRERROR_R_RETURNS_CHAR_WITH_GNU_SOURCE], [ ])
+fi
+
 dnl ============================================================================
 dnl Check for typedefs, structures, and compiler characteristics.
 AC_HEADER_STDBOOL

include/jemalloc/internal/jemalloc_internal_defs.h.in

@@ -358,4 +358,9 @@
 /* If defined, jemalloc takes the malloc/free/etc. symbol names. */
 #undef JEMALLOC_IS_MALLOC
 
+/*
+ * Defined if strerror_r returns char * if _GNU_SOURCE is defined.
+ */
+#undef JEMALLOC_STRERROR_R_RETURNS_CHAR_WITH_GNU_SOURCE
+
 #endif /* JEMALLOC_INTERNAL_DEFS_H_ */

src/malloc_io.c

@@ -111,7 +111,7 @@ buferror(int err, char *buf, size_t buflen) {
 	FormatMessageA(FORMAT_MESSAGE_FROM_SYSTEM, NULL, err, 0,
 	    (LPSTR)buf, (DWORD)buflen, NULL);
 	return 0;
-#elif defined(__GLIBC__) && defined(_GNU_SOURCE)
+#elif defined(JEMALLOC_STRERROR_R_RETURNS_CHAR_WITH_GNU_SOURCE) && defined(_GNU_SOURCE)
 	char *b = strerror_r(err, buf, buflen);
 	if (b != buf) {
 		strncpy(buf, b, buflen);