Detect msys/gcc in configure script. Fixes #936

configure.ac

@@ -155,14 +155,15 @@ AS_IF([test "$ax_cv_prog_bison" = "yes"],
               AX_APPEND_FLAG([-Wcounterexamples], [EXTRA_YFLAGS])],
              [AC_MSG_RESULT([no])])])
 
-AX_PROG_FLEX([], [AC_MSG_ERROR(Flex not found)])
+AX_PROG_FLEX([], [AC_MSG_ERROR([Flex not found])])
 
 case $host_os in
   *cygwin*|msys*|mingw32*)
     LIBS="$LIBS -ldbghelp -lwsock32"   # For StackTrace64 and sockets
     DIR_SEP=\\\\
     pathprog="cygpath -m"
     AC_CHECK_PROG([CANDLE], [candle], [yes])   # For WiX installer
+    NVC_CHECK_MSYS
     ;;
   *)
     AC_SEARCH_LIBS([dlopen], [dl dld], [], [

m4/nvc.m4

@@ -2,17 +2,41 @@ dnl Check whether TLS is emulated.
 dnl Adapted from https://github.com/gcc-mirror/gcc/blob/0f1727e25f/config/tls.m4
 AC_DEFUN([NVC_CHECK_EMUTLS], [
   AC_CACHE_CHECK([whether the thread-local storage support is from emutls],
-  		 nvc_cv_use_emutls, [
+                 nvc_cv_use_emutls, [
     nvc_cv_use_emutls=no
     echo '__thread int a; int b; int main() { return a = b; }' > conftest.c
     if AC_TRY_COMMAND(${CC-cc} -Werror -S -o conftest.s conftest.c 1>&AS_MESSAGE_LOG_FD); then
       if grep __emutls_get_address conftest.s > /dev/null; then
-	nvc_cv_use_emutls=yes
+        nvc_cv_use_emutls=yes
       fi
     fi
     rm -f conftest.*
     ])
   if test "$nvc_cv_use_emutls" = "yes" ; then
     AC_DEFINE(USE_EMUTLS, 1,
-      	      [Define to 1 if the target uses emutls for thread-local storage.])
+              [Define to 1 if the target uses emutls for thread-local storage.])
   fi])
+
+dnl Ensure we are not building in the MSYS environment
+AC_DEFUN([NVC_CHECK_MSYS], [
+  AC_MSG_CHECKING([if $CC is the MSYS compiler])
+  AS_IF([$CC -dumpmachine | grep -q pc-msys],
+        [AC_MSG_RESULT([yes])
+         case "$MSYSTEM" in
+           CLANG64)
+             AC_MSG_ERROR([$CC is msys/gcc which is not supported: install mingw-w64-clang-x86_64-clang or pass CC=clang])
+             ;;
+           UCRT64)
+             AC_MSG_ERROR([$CC is msys/gcc which is not supported: install mingw-w64-ucrt-x86_64-gcc])
+             ;;
+           MINGW64)
+             AC_MSG_ERROR([$CC is msys/gcc which is not supported: install mingw-w64-x86_64-gcc])
+             ;;
+           MSYS)
+             AC_MSG_ERROR([$CC is msys/gcc which is not supported])
+             ;;
+           *)
+             AC_MSG_ERROR([$CC is msys/gcc which is not supported: install the native compiler for $MSYSTEM])
+             ;;
+         esac],
+        [AC_MSG_RESULT([no])])])