update preprocessor #defines

this ensures that -DARDUINO={runtime.ide.version} is defined at the preprocessor step as well

Author: oclyke

platform.txt

@@ -14,7 +14,7 @@ defines.mbed=-DMBED_NO_GLOBAL_USING_DIRECTIVE
 defines.variant={build.defines}
 defines.extra=
 defines.all={defines.variant} {defines.arduino} {defines.mbed} {defines.extra} -DCORDIO_ZERO_COPY_HCI
-defines.preproc={defines.mbed.cxx}
+defines.preproc={defines.all}
 defines.asm={defines.all} @{build.variant.path}/mbed/.asm-symbols
 defines.c={defines.all} @{build.variant.path}/mbed/.c-symbols
 defines.cxx={defines.all} @{build.variant.path}/mbed/.cxx-symbols