Patch to build mipcalc on Windows with MinGW-w64

[Stephen Kitt]

Hi,

All MinGW targets require underscores when linking. This patch fixes
acinclude.m4 and the resulting configure so they don't limit the use of
underscores to the old mingw32msvc targets; otherwise the build fails if
libgomp is available and an attempt is made to build mpicalc.exe.

Regards,

Stephen

Signed-off-by: Stephen Kitt <steve at sk2.org>

--- a/acinclude.m4
+++ b/acinclude.m4
@@ -692,7 +692,7 @@
 AC_DEFUN([GNUPG_SYS_SYMBOL_UNDERSCORE],
 [tmp_do_check="no"
 case "${host}" in
-    *-mingw32msvc*)
+    *-mingw32*)
         ac_cv_sys_symbol_underscore=yes
         ;;
     i386-emx-os2 | i[3456]86-pc-os2*emx | i386-pc-msdosdjgpp)
--- a/configure
+++ b/configure
@@ -7314,7 +7314,7 @@
 
 tmp_do_check="no"
 case "${host}" in
-    *-mingw32msvc*)
+    *-mingw32*)
         ac_cv_sys_symbol_underscore=yes
         ;;
     i386-emx-os2 | i345686-pc-os2*emx | i386-pc-msdosdjgpp)