compiler.h: add __weak macro

Instead of writing out '__attribute__((weak))' use a shorter form.

Change-Id: If418a1d55052780077febd2d8f2089021f414b91
Signed-off-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-on: https://review.coreboot.org/25767
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Arthur Heymans <arthur@aheymans.xyz>
Reviewed-by: Justin TerAvest <teravest@chromium.org>

src/soc/amd/stoneyridge/BiosCallOuts.c

@@ -15,6 +15,7 @@
  * GNU General Public License for more details.
  */
 
+#include <compiler.h>
 #include <device/device.h>
 #include <device/pci_def.h>
 #include <amdblocks/BiosCallOuts.h>
@@ -28,7 +29,7 @@
 #include "chip.h"
 #include <amdblocks/car.h>
 
-void __attribute__((weak)) platform_FchParams_reset(
+void __weak platform_FchParams_reset(
 				FCH_RESET_DATA_BLOCK *FchParams_reset) {}
 
 AGESA_STATUS agesa_fch_initreset(UINT32 Func, UINTN FchData, VOID *ConfigPtr)
@@ -159,7 +160,7 @@ AGESA_STATUS agesa_HaltThisAp(UINT32 Func, UINTN Data, VOID *ConfigPtr)
 }
 
 /* Allow mainboards to fill the SPD buffer */
-__attribute__((weak)) int mainboard_read_spd(uint8_t spdAddress, char *buf,
+__weak int mainboard_read_spd(uint8_t spdAddress, char *buf,
 						size_t len)
 {
 	printk(BIOS_DEBUG, "WEAK: %s/%s called\n", __FILE__, __func__);