Fix up feature test macros

Move all feature test macros to the start of the file and check that
they aren't already defined or defined to a lower value than the file
needs.

Projects should be allowed to put these in CFLAGS and we shouldn't break
when they do.

src/core/iomgr/resolve_address.c

@@ -31,7 +31,9 @@
  *
  */
 
+#ifndef _POSIX_SOURCE
 #define _POSIX_SOURCE
+#endif
 
 #include "src/core/iomgr/sockaddr.h"
 #include "src/core/iomgr/resolve_address.h"

src/core/iomgr/socket_utils_linux.c

@@ -31,7 +31,9 @@
  *
  */
 
+#ifndef _GNU_SOURCE
 #define _GNU_SOURCE
+#endif
 #include <grpc/support/port_platform.h>
 
 #ifdef GPR_LINUX

src/core/iomgr/socket_utils_posix.c

@@ -35,7 +35,6 @@
 
 #ifdef GPR_POSIX_SOCKETUTILS
 
-#define _BSD_SOURCE
 #include "src/core/iomgr/socket_utils_posix.h"
 
 #include <fcntl.h>

src/core/iomgr/tcp_server_posix.c

@@ -31,11 +31,15 @@
  *
  */
 
+/* FIXME: "posix" files shouldn't be depending on _GNU_SOURCE */
+#ifndef _GNU_SOURCE
+#define _GNU_SOURCE
+#endif
+
 #include <grpc/support/port_platform.h>
 
 #ifdef GPR_POSIX_SOCKET
 
-#define _GNU_SOURCE
 #include "src/core/iomgr/tcp_server.h"
 
 #include <limits.h>

src/core/support/log_linux.c

@@ -31,8 +31,14 @@
  *
  */
 
+#ifndef _POSIX_SOURCE
 #define _POSIX_SOURCE
+#endif
+
+#ifndef _GNU_SOURCE
 #define _GNU_SOURCE
+#endif
+
 #include <grpc/support/port_platform.h>
 
 #ifdef GPR_LINUX

src/core/support/log_posix.c

@@ -31,11 +31,16 @@
  *
  */
 
-#ifndef _POSIX_C_SOURCE
+#if !defined _POSIX_C_SOURCE || _POSIX_C_SOURCE < 200112L
+#undef _POSIX_C_SOURCE
 #define _POSIX_C_SOURCE 200112L
 #endif
 
+/* FIXME: "posix" files probably shouldn't depend on _GNU_SOURCE */
+#ifndef _GNU_SOURCE
 #define _GNU_SOURCE
+#endif
+
 #include <grpc/support/port_platform.h>
 
 #if defined(GPR_POSIX_LOG)

src/core/support/string_posix.c

@@ -33,7 +33,8 @@
 
 /* Posix code for gpr snprintf support. */
 
-#ifndef _POSIX_C_SOURCE
+#if !defined _POSIX_C_SOURCE || _POSIX_C_SOURCE < 200112L
+#undef _POSIX_C_SOURCE
 #define _POSIX_C_SOURCE 200112L
 #endif
 

test/core/echo/echo_test.c

@@ -31,7 +31,10 @@
  *
  */
 
+#ifndef _POSIX_SOURCE
 #define _POSIX_SOURCE
+#endif
+
 #include <unistd.h>
 #include <assert.h>
 #include <stdio.h>

test/core/fling/fling_stream_test.c

@@ -31,7 +31,10 @@
  *
  */
 
+#ifndef _POSIX_SOURCE
 #define _POSIX_SOURCE
+#endif
+
 #include <unistd.h>
 #include <assert.h>
 #include <stdio.h>

test/core/fling/fling_test.c

@@ -31,7 +31,10 @@
  *
  */
 
+#ifndef _POSIX_SOURCE
 #define _POSIX_SOURCE
+#endif
+
 #include <unistd.h>
 #include <assert.h>
 #include <stdio.h>