Memory leaks in the test programs run by configure when using GTK 2
result in configuration failures when using -fsanitize=address in
{CXX,LD}FLAGS, so fix these leaks to allow configuring using
"CXXFLAGS=-fsanitize=address LDFLAGS=-fsanitize=address" together with
--with-gtk=2 (this already worked correctly with the default GTK 3).
Closes https://github.com/wxWidgets/wxWidgets/pull/2001
Use the macro versions from 2.24.29 and 3.18.8 (latest available in Debian for
GTK+ 2 and 3 respectively) to fix the detection of pkg-config which was
incorrect in the old gtk-2.0.m4.
Closes#17027.
