build: prereq-build.mk: fix gcc/g++ SetupHostCommand invocation

A missing comma caused the first command option to be considered part of
the error message.

Signed-off-by: Jo-Philipp Wich <jo@mein.io>

include/prereq-build.mk

@@ -27,7 +27,7 @@ $(eval $(call TestHostCommand,proper-umask, \
 	umask | grep -xE 00[012][012]))
 
 $(eval $(call SetupHostCommand,gcc, \
-	Please install the GNU C Compiler (gcc) 4.8 or later \
+	Please install the GNU C Compiler (gcc) 4.8 or later, \
 	$(CC) -dumpversion | grep -E '^(4\.[8-9]|[5-9]\.?)', \
 	gcc -dumpversion | grep -E '^(4\.[8-9]|[5-9]\.?)', \
 	gcc48 --version | grep gcc, \
@@ -46,7 +46,7 @@ $(eval $(call TestHostCommand,working-gcc, \
 		gcc -x c -o $(TMP_DIR)/a.out -))
 
 $(eval $(call SetupHostCommand,g++, \
-	Please install the GNU C++ Compiler (g++) 4.8 or later \
+	Please install the GNU C++ Compiler (g++) 4.8 or later, \
 	$(CXX) -dumpversion | grep -E '^(4\.[8-9]|[5-9]\.?)', \
 	g++ -dumpversion | grep -E '^(4\.[8-9]|[5-9]\.?)', \
 	g++48 --version | grep g++, \