Fix linking to self-built deps on Windows + Clang

1) Expat: 'MD' suffix is added on MSVC only, 'd' suffix is added on WIN32
2) ZLib: 'd' suffix is added only on MSVC

Author: dimula73

share/cmake/modules/install/InstallZLIB.cmake

@@ -53,8 +53,8 @@ if(NOT ZLIB_FOUND AND OCIO_INSTALL_EXT_PACKAGES AND NOT OCIO_INSTALL_EXT_PACKAGE
 
     set(ZLIB_INCLUDE_DIRS "${_EXT_DIST_ROOT}/${CMAKE_INSTALL_INCLUDEDIR}")
 
-    # Windows need the "d" suffix at the end.
-    if(WIN32 AND BUILD_TYPE_DEBUG)
+    # Windows need the "d" suffix at the end (only for MSVC).
+    if(MSVC AND BUILD_TYPE_DEBUG)
         set(_ZLIB_LIB_SUFFIX "d")
     endif()
 

share/cmake/modules/install/Installexpat.cmake

@@ -46,9 +46,11 @@ if(NOT expat_FOUND AND OCIO_INSTALL_EXT_PACKAGES AND NOT OCIO_INSTALL_EXT_PACKAG
         if(BUILD_TYPE_DEBUG)
             set(_expat_LIB_SUFFIX "d")
         endif()
-        # Static Linking, Multi-threaded Dll naming (>=2.2.8):
-        #   https://github.com/libexpat/libexpat/blob/R_2_2_8/expat/win32/README.txt
-        set(_expat_LIB_SUFFIX "${_expat_LIB_SUFFIX}MD")
+        if (MSVC)
+            # Static Linking, Multi-threaded Dll naming (>=2.2.8):
+            #   https://github.com/libexpat/libexpat/blob/R_2_2_8/expat/win32/README.txt
+            set(_expat_LIB_SUFFIX "${_expat_LIB_SUFFIX}MD")
+        endif()
     endif()
 
     # Expat use a hardcoded lib prefix instead of CMAKE_STATIC_LIBRARY_PREFIX