giga: m4: apply the correct includes

Author: facchinm

boards.txt

@@ -739,7 +739,7 @@ giga.compiler.mbed.defines={build.variant.path}/defines.txt
 giga.compiler.mbed.ldflags={build.variant.path}/ldflags.txt
 giga.compiler.mbed.cflags={build.variant.path}/cflags.txt
 giga.compiler.mbed.cxxflags={build.variant.path}/cxxflags.txt
-giga.compiler.mbed.includes={build.variant.path}/includes.txt
+giga.compiler.mbed.includes={build.variant.path}/../GIGA/includes.txt
 giga.compiler.mbed.extra_ldflags=-lstdc++ -lsupc++ -lm -lc -lgcc -lnosys
 giga.compiler.mbed="{build.variant.path}/libs/libmbed.a"
 giga.vid.0=0x2341