Fix mingw build on ubuntu 20.04

- Link libssp to resolve undefined reference __memcpy_chk
- Disable dtlstest since mingw does not have poll

m4/check-os-options.m4

@@ -112,7 +112,7 @@ char buf[1]; getentropy(buf, 1);
 		CPPFLAGS="$CPPFLAGS -D_REENTRANT -D_POSIX_THREAD_SAFE_FUNCTIONS"
 		CPPFLAGS="$CPPFLAGS -DWIN32_LEAN_AND_MEAN -D_WIN32_WINNT=0x0600"
 		CPPFLAGS="$CPPFLAGS"
-		AC_SUBST([PLATFORM_LDADD], ['-lws2_32 -lbcrypt'])
+		AC_SUBST([PLATFORM_LDADD], ['-lws2_32 -lbcrypt -lssp'])
 		;;
 	*solaris*)
 		HOST_OS=solaris

tests/Makefile.am

@@ -172,9 +172,11 @@ check_PROGRAMS += dsatest
 dsatest_SOURCES = dsatest.c
 
 # dtlstest
+if !HOST_WIN
 TESTS += dtlstest.sh
 check_PROGRAMS += dtlstest
 dtlstest_SOURCES = dtlstest.c
+endif
 EXTRA_DIST += dtlstest.sh
 
 # ec_point_conversion