Merge branch 'libwebp' of github.com:cjmayo/wxWidgets

CMake: Support finding system libwebp using pkg-config too,

See #25763.

build/cmake/lib/webp.cmake

@@ -69,6 +69,4 @@ if(wxUSE_LIBWEBP STREQUAL "builtin")
         )
     endif()
 
-elseif(wxUSE_LIBWEBP)
-    find_package(WebP REQUIRED)
 endif()

build/cmake/modules/FindWebP.cmake

@@ -0,0 +1,8 @@
+find_package(WebP CONFIG)
+
+if(NOT WebP_FOUND)
+    find_package(PkgConfig QUIET)
+    if(PKG_CONFIG_FOUND)
+        pkg_check_modules(WebP libwebp)
+    endif()
+endif()