prog_loader: Play nice with gc-sections

With an x86_64-elf toolchain, this code that is unused
outside of ramstage, is causing undefined references.

Help the compiler along a little bit by conditionally compiling
the code in ramstage only.

Change-Id: I75518149b53c24eda4b985b0fef856447e196dec
Signed-off-by: Stefan Reinauer <stefan.reinauer@coreboot.org>
Reviewed-on: http://review.coreboot.org/10585
Tested-by: build bot (Jenkins)
Reviewed-by: Patrick Georgi <pgeorgi@google.com>

src/lib/prog_loaders.c

@@ -121,6 +121,8 @@ fail:
 	die("Ramstage was not loaded!\n");
 }
 
+#ifdef __RAMSTAGE__ // gc-sections should take care of this
+
 static struct prog global_payload =
 	PROG_INIT(ASSET_PAYLOAD, CONFIG_CBFS_PREFIX "/payload");
 
@@ -170,3 +172,5 @@ void payload_run(void)
 
 	prog_run(payload);
 }
+
+#endif