Fix mingw-w64:llvm-mingw error: unknown type name 'pthread_t' (#653)

* Include <pthread.h> in astc_encode.cpp for non Windows and WIN32_HAS_PTHREADS.
* Fix test for setting WIN32_HAS_PTHREADS to set only when pthreads found.
* Fix duplicate definition warnings for KTX_API when building static library for Windows.

Fixes #651.

CMakeLists.txt

@@ -314,7 +314,6 @@ macro(commom_lib_settings lib write)
     )
 
     if( LIB_TYPE STREQUAL STATIC )
-        # KHRONOS_STATIC overrides the value of KTX_API set below.
         target_compile_definitions(${lib} PUBLIC KHRONOS_STATIC)
     endif()
 
@@ -340,9 +339,8 @@ macro(commom_lib_settings lib write)
         target_compile_definitions(
             ${lib}
         PRIVATE
-            # KHRONOS_STATIC defined earlier for the static library overrides
-            # so no need for a generator expression to conditionally set this.
-            KTX_API=__declspec\(dllexport\)
+            # Only set dllexport when building a shared library.
+            $<$<STREQUAL:${LIB_TYPE},SHARED>:KTX_API=__declspec\(dllexport\)>
         PUBLIC # only for basisu_c_binding.
             BASISU_NO_ITERATOR_DEBUG_LEVEL
         )
@@ -405,7 +403,7 @@ macro(commom_lib_settings lib write)
         if(MINGW)
             # Check if the Threads package is provided; if using Mingw it MIGHT be
             find_package(Threads)
-            if(Threads_FOUND)
+            if(Threads_FOUND AND CMAKE_USE_PTHREADS_INIT)
                 target_compile_definitions(ktx PRIVATE WIN32_HAS_PTHREADS)
                 target_link_libraries(ktx PRIVATE Threads::Threads)
             endif()

lib/astc_encode.cpp

@@ -34,9 +34,10 @@
 
 #include "astc-encoder/Source/astcenc.h"
 
+#if !defined(_WIN32) || defined(WIN32_HAS_PTHREADS)
+#include <pthread.h>
+#else
 // Provide pthreads support on windows
-#if defined(_WIN32) && !defined(WIN32_HAS_PTHREADS)
-
 #define WIN32_LEAN_AND_MEAN
 #include <Windows.h>
 
@@ -60,7 +61,6 @@ pthread_join(pthread_t thread, void** value) {
     WaitForSingleObject(thread, INFINITE);
     return 0;
 }
-
 #endif
 
 static astcenc_image*