Fixing support for mingw toolchains that target the newer ucrt (Khron…

…osGroup#642)

Fixes KhronosGroup#641.

CMakeLists.txt

@@ -356,6 +356,12 @@ macro(commom_lib_settings lib write)
                 lib/internalexport_mingw.def
                 $<${write}:lib/internalexport_write_mingw.def>
             )
+            # Need these flags if mingw happens to target the ucrt (new) rather 
+            # than the legacy msvcrt. Otherwise tests will fail to run because
+            # the necessary dlls will be missing. If we statically link 
+            # them instead it's fine. This does not cause any abberations if 
+            # the mingw toolchain targets msvcrt instead.
+            target_link_options(${lib} PUBLIC -static-libgcc -static-libstdc++)
         else()
             target_sources(
                 ${lib}

lib/filestream.c

@@ -307,13 +307,13 @@ KTX_error_code ktxFileStream_getsize(ktxStream* str, ktx_size_t* size)
 
     assert(str->type == eStreamTypeFile);
 
-    // Need to flush so that fstat will return the current size.
-    // Can ignore return value. The only error that can happen is to tell you
-    // it was a NOP because the file is read only.
-#if (defined(_MSC_VER) && _MSC_VER < 1900) || defined(__MINGW32__)
-    // Bug in VS2013 msvcrt. fflush on FILE open for READ changes file offset
-    // to 4096.
-    if (str->data.file->_flag & _IOWRT)
+  // Need to flush so that fstat will return the current size.
+  // Can ignore return value. The only error that can happen is to tell you
+  // it was a NOP because the file is read only.
+#if (defined(_MSC_VER) && _MSC_VER < 1900) || defined(__MINGW64__) && !defined(_UCRT)
+  // Bug in VS2013 msvcrt. fflush on FILE open for READ changes file offset
+  // to 4096.
+  if (str->data.file->_flag & _IOWRT)
 #endif
     (void)fflush(str->data.file);
     statret = fstat(fileno(str->data.file), &statbuf);