run_imp: allow to specify mingw

diff --git a/run_imp.sh b/run_imp.sh
index 7c542be..665b3f9 100755 (executable)
--- a/run_imp.sh
+++ b/run_imp.sh
@@ -1,6 +1,8 @@
 #!/bin/sh
 
-mingwb=i686-w64-mingw32
+# warning: i686-w64-mingw32- on Ubuntu 14.04
+# contains broken InterlockedDecrement
+test -n "$mingwb" || mingwb=i686-w64-mingw32
 
 target_s=$1
 src_asm=$2