Rewrite the check for windows and MinGW.

It is recommended that AC_CYGWIN not be used and under MinGW
the previous test was complaining about multiple calls to
AC_CANONICAL_HOST. The new test performs the same function
and also displays the MinGW status if we are compiling on
windows.

Also removed a AX_CCP_IDENT call in the vpi directory and
tgt-null is built by the top configure so there is no need
to try to run configure in that directory.

aclocal.m4

@@ -64,17 +64,22 @@ fi
 # Combined check for several flavors of Microsoft Windows so
 # their "issues" can be dealt with
 AC_DEFUN([AX_WIN32],
-[AC_CYGWIN
-AC_MINGW32
-WIN32=no
-AC_MSG_CHECKING([for Microsoft Windows])
-if test "$CYGWIN" = "yes" -o "$MINGW32" = "yes"
-then
-    WIN32=yes
-fi
+[AC_MSG_CHECKING([for Microsoft Windows])
+AC_REQUIRE([AC_CANONICAL_HOST]) []dnl
+case $host_os in
+     *cygwin*) MINGW32=no;  WIN32=yes;;
+
+      *mingw*) MINGW32=yes; WIN32=yes;;
+
+            *) MINGW32=no;  WIN32=no;;
+esac
 AC_SUBST(MINGW32)
 AC_SUBST(WIN32)
 AC_MSG_RESULT($WIN32)
+if test $WIN32 = yes; then
+AC_MSG_CHECKING([for MinGW])
+AC_MSG_RESULT($MINGW32)
+fi
 ])# AX_WIN32
 
 # AX_LD_EXTRALIBS

configure.in

@@ -122,6 +122,6 @@ AX_C_UNDERSCORES_TRAILING
 #######################
 
 # XXX disable tgt-fpga for the moment
-AC_CONFIG_SUBDIRS(vvp vpi tgt-stub tgt-null tgt-vvp tgt-vhdl libveriuser cadpli)
+AC_CONFIG_SUBDIRS(vvp vpi tgt-stub tgt-vvp tgt-vhdl libveriuser cadpli)
 
 AC_OUTPUT(Makefile ivlpp/Makefile driver/Makefile driver-vpi/Makefile tgt-null/Makefile tgt-verilog/Makefile tgt-pal/Makefile)

vpi/configure.in

@@ -29,8 +29,6 @@ AC_SUBST(EXEEXT)
 # Combined check for Microsoft-related bogosities; sets WIN32 if found
 AX_WIN32
 
-AX_CPP_IDENT
-
 AC_CHECK_HEADERS(malloc.h inttypes.h)
 
 AC_CHECK_LIB(z, gzwrite)