configure: Set __MSVCRT_VERSION__to 0x0700 for MinGW

This exposes some required functionality like _aligned_malloc() in the
MinGW system headers, thus obviating the need for the memalign hack.

configure

@@ -4003,6 +4003,8 @@ probe_libc(){
             (__MINGW32_MAJOR_VERSION == 3 && __MINGW32_MINOR_VERSION >= 15)" ||
             die "ERROR: MinGW32 runtime version must be >= 3.15."
         add_${pfx}cppflags -U__STRICT_ANSI__ -D__USE_MINGW_ANSI_STDIO=1
+        check_${pfx}cpp_condition _mingw.h "__MSVCRT_VERSION__ < 0x0700__" &&
+            add_${pfx}cppflags -D__MSVCRT_VERSION__=0x0700
         eval test \$${pfx_no_}cc_type = "gcc" &&
             add_${pfx}cppflags -D__printf__=__gnu_printf__
     elif check_${pfx}cpp_condition crtversion.h "defined _VC_CRT_MAJOR_VERSION"; then