Makefile: disable some warnings for GCC 8.x

.travis.yml

@@ -85,7 +85,7 @@ matrix:
               - p7zip-full
               - gcc-8
           compiler: gcc-8
-          env: WFLAGS="-Wno-tautological-compare -Wno-error=implicit-fallthrough -Wimplicit-fallthrough=3"
+          env: WFLAGS="-Wno-tautological-compare -Wno-error=implicit-fallthrough -Wimplicit-fallthrough=3 -Wno-error=format-overflow"
           #gcc-8 (Ubuntu 7.2.0-1ubuntu1~14.04) 8.1.0
         - os: linux
           compiler: clang

src/Makefile.cfg

@@ -222,6 +222,14 @@ endif
 ifdef GCC61
  WFLAGS+=-Wno-tautological-compare -Wno-error=tautological-compare
 endif
+ifdef GCC80
+ WFLAGS+=-Wno-error=format-overflow
+ WFLAGS+=-Wno-error=stringop-truncation
+ WFLAGS+=-Wno-error=stringop-overflow
+ WFLAGS+=-Wno-format-overflow
+ WFLAGS+=-Wno-stringop-truncation
+ WFLAGS+=-Wno-stringop-overflow
+endif
 
 
 #indicate platform and what interface use with