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>
diff --git a/src/soc/intel/common/block/lpc/lpc.c b/src/soc/intel/common/block/lpc/lpc.c
index 079ecde..c462d9d 100644
--- a/src/soc/intel/common/block/lpc/lpc.c
+++ b/src/soc/intel/common/block/lpc/lpc.c
@@ -14,6 +14,7 @@
  * GNU General Public License for more details.
  */
 
+#include <compiler.h>
 #include <device/device.h>
 #include <device/pci.h>
 #include <device/pci_ids.h>
@@ -24,13 +25,13 @@
 /* SoC overrides */
 
 /* Common weak definition, needs to be implemented in each soc LPC driver. */
-__attribute__((weak)) void lpc_soc_init(struct device *dev)
+__weak void lpc_soc_init(struct device *dev)
 {
 	/* no-op */
 }
 
 /* Fill up LPC IO resource structure inside SoC directory */
-__attribute__((weak)) void pch_lpc_soc_fill_io_resources(struct device *dev)
+__weak void pch_lpc_soc_fill_io_resources(struct device *dev)
 {
 	/* no-op */
 }