Fix a FTCBFS issue because of using AC_PATH_PROG

Fix a FTCBFS issue because of using AC_PATH_PROG

Bug-Debian: https://bugs.debian.org/895996
Last-Update: 2025-07-11

This patch fixes a FTCBFS issue caused by using AC_PATH_PROG to
discover the location of pkg-config, which fails to select the
correct version on cross-compilations. The corresponding lintian
warning 'autotools-pkg-config-macro-not-cross-compilation-safe'
suggests to use PKG_PROG_PKG_CONFIG and $PKG_CONFIG instead.

Gbp-Pq: Name cross.patch