build, imagebuilder: Do not require compilers

The buildroot and SDK both require the compilers (gcc, g++) to be
installed on the host system, however the ImageBuilder uses precompiled
binaries.

This patch changes the prerequirements checks to skip the checking for
the compilers if running as ImageBuilder. A similar change has been
made for libncurses-dev in 4a1a58a3e2d2.

Signed-off-by: Sven Roederer <devel-sven@geroedel.de>
Acked-by: Paul Spooren <mail@aparcar.org>
(cherry picked from commit ae12a747cae3df16d84b7dc92f39427948d4e8e2)

include/prereq-build.mk

@@ -26,6 +26,7 @@ $(eval $(call TestHostCommand,proper-umask, \
 	Please build with umask 022 - other values produce broken packages, \
 	umask | grep -xE 0?0[012][012]))
 
+ifndef IB
 $(eval $(call SetupHostCommand,gcc, \
 	Please install the GNU C Compiler (gcc) 4.8 or later, \
 	$(CC) -dumpversion | grep -E '^(4\.[8-9]|[5-9]\.?|10\.?)', \
@@ -37,7 +38,9 @@ $(eval $(call TestHostCommand,working-gcc, \
 	it appears to be broken, \
 	echo 'int main(int argc, char **argv) { return 0; }' | \
 		gcc -x c -o $(TMP_DIR)/a.out -))
+endif
 
+ifndef IB
 $(eval $(call SetupHostCommand,g++, \
 	Please install the GNU C++ Compiler (g++) 4.8 or later, \
 	$(CXX) -dumpversion | grep -E '^(4\.[8-9]|[5-9]\.?|10\.?)', \
@@ -50,6 +53,7 @@ $(eval $(call TestHostCommand,working-g++, \
 	echo 'int main(int argc, char **argv) { return 0; }' | \
 		g++ -x c++ -o $(TMP_DIR)/a.out - -lstdc++ && \
 		$(TMP_DIR)/a.out))
+endif
 
 ifndef IB
 $(eval $(call TestHostCommand,ncurses, \