Enable use of the PCRE2 library on Windows

- windows/MYconfigure

Use the PCRE2 library for building Privoxy on Windows.

- configure.in

PCRE2_STATIC must be defined if you want to statically link the PCRE2 library.
If it isn't defined you'll get these kind of linker errors:
 undefined reference to `_imp__pcre2_compile_8'
 undefined reference to `_imp__pcre2_jit_compile_8'
 undefined reference to `_imp__pcre2_match_data_create_from_pattern_8'
 undefined reference to `_imp__pcre2_match_8'