FindPkgConfig: Search for pkg-config.bat file on a Windows host

The strawberry perl distribution ships a pkg-config file and a
pkg-config.bat file.

find_program() does not usually look for a .bat file program unless
explicitly specified in the NAMES argument. This would cause
CMake to find the non-bat file, and executing that with
execute_process() leads to a
'%1 is not a valid Win32 application' error.

Prefer to search for pkg-config.bat file when on a Windows host, in
additiona to the regular pkg-config file.

Fixes: #21239

Modules/FindPkgConfig.cmake

@@ -31,7 +31,13 @@ set(PKG_CONFIG_VERSION 1)
 if((NOT PKG_CONFIG_EXECUTABLE) AND (NOT "$ENV{PKG_CONFIG}" STREQUAL ""))
   set(PKG_CONFIG_EXECUTABLE "$ENV{PKG_CONFIG}" CACHE FILEPATH "pkg-config executable")
 endif()
-find_program(PKG_CONFIG_EXECUTABLE NAMES pkg-config DOC "pkg-config executable")
+
+set(PKG_CONFIG_NAMES "pkg-config")
+if(CMAKE_HOST_WIN32)
+  list(PREPEND PKG_CONFIG_NAMES "pkg-config.bat")
+endif()
+
+find_program(PKG_CONFIG_EXECUTABLE NAMES ${PKG_CONFIG_NAMES} DOC "pkg-config executable")
 mark_as_advanced(PKG_CONFIG_EXECUTABLE)
 
 set(_PKG_CONFIG_FAILURE_MESSAGE "")