Update gcc.py for preprocessing in linker script

To fix https://github.com/ARMmbed/mbed-os/issues/11214, we need this update. :-)

tools/toolchains/gcc.py

@@ -248,6 +248,7 @@ class GCC(mbedToolchain):
             preproc_output = join(dirname(output), ".link_script.ld")
             cmd = (
                 self.preproc + [mem_map] + self.ld[1:] + ["-o", preproc_output]
+                self.get_compile_options(self.get_symbols(), [])
             )
             self.notify.cc_verbose("Preproc: %s" % ' '.join(cmd))
             self.default_cmd(cmd)