sysmobts: Change the compiler-gcc*.h to work with gcc5,6,7 and later

In the past I copy and pasted the compiler-gcc4.h to have gcc-5.h and
gcc-6.h suffix. I didn't want to do the same for gcc7 and cherry picked
the original commit. Not compile tested though.

recipes-bsp/barebox/barebox-sysmobts_git.bb

@@ -1,6 +1,6 @@
 require barebox.inc
 
-SRCREV = "1d8bdd6f226df2ecbde3776b52fbc228158293fd"
+SRCREV = "d87c27d7ab143d58f358df5722be2b9675103d2e"
 SRC_URI = " \
 	git://git.sysmocom.de/barebox.git;branch=v2015.06 \
 	file://defconfig \