Normalize IS_MINGW checks (and include MSYS, like main Makefile) (#1318)

Following in the steps of #1290
diff --git a/cstool/Makefile b/cstool/Makefile
index ec62751..5410fa3 100644
--- a/cstool/Makefile
+++ b/cstool/Makefile
@@ -19,7 +19,7 @@
 ifeq ($(IS_CYGWIN),1)
 LIBCAPSTONE = capstone.lib
 else
-IS_MINGW := $(shell $(CC) --version 2>/dev/null | grep -i mingw | wc -l)
+IS_MINGW := $(shell $(CC) --version 2>/dev/null | grep -i "\(mingw\|MSYS\)" | wc -l)
 ifeq ($(IS_MINGW),1)
 LIBCAPSTONE = capstone.lib
 endif
diff --git a/tests/Makefile b/tests/Makefile
index d3c392a..0ec4054 100644
--- a/tests/Makefile
+++ b/tests/Makefile
@@ -44,7 +44,7 @@
 AR_EXT = lib
 else
 # mingw?
-IS_MINGW := $(shell $(CC) --version | grep -i mingw | wc -l)
+IS_MINGW := $(shell $(CC) --version 2>/dev/null | grep -i "\(mingw\|MSYS\)" | wc -l)
 ifeq ($(IS_MINGW),1)
 CFLAGS := $(CFLAGS:-fPIC=)
 BIN_EXT = .exe