Introduce environment variable UPX_DISABLE_GITREV_WARNING.

.github/travis_testsuite_1.sh

@@ -168,6 +168,7 @@ if [[ $BM_B =~ (^|\+)coverage($|\+) ]]; then
 fi
 
 export UPX="--prefer-ucl --no-color --no-progress"
+export UPX_DISABLE_GITREV_WARNING=1
 
 # let's go
 if ! $upx_run --version;          then echo "UPX-ERROR: FATAL: upx --version FAILED"; exit 1; fi

src/main.cpp

@@ -1539,6 +1539,12 @@ int __acc_cdecl_main main(int argc, char *argv[])
     do_files(i,argc,argv);
 
     if (gitrev[0])
+    {
+        bool warn = true;
+        const char *ee = getenv("UPX_DISABLE_GITREV_WARNING");
+        if (ee && ee[0] && strcmp(ee, "1") == 0)
+            warn = false;
+        if (warn)
         {
             FILE *f = stdout;
             int fg = con_fg(f, FG_RED);
@@ -1546,6 +1552,7 @@ int __acc_cdecl_main main(int argc, char *argv[])
             fg = con_fg(f, fg);
             UNUSED(fg);
         }
+    }
 
 #if 0 && defined(__GLIBC__)
     //malloc_stats();