Revert "Disable use of build system pkg-config files when cross-compiling"

This reverts commit 893ebbab0c because it
breaks cross-compiling using target-specific pkg-config installed on the
main system, which is a perfectly legitimate use case.

To avoid the original problem fixed by that commit, PKG_CONFIG_LIBDIR
needs to be set manually before running configure when using host
pkg-config -- but not when using target pkg-config.

Closes #22886.

configure

@@ -25188,15 +25188,6 @@ $as_echo "no" >&6; }
 
 fi
 
-if test "$build" != "$host"; then
-
-
-                if test -z "$PKG_CONFIG_LIBDIR"; then
-        PKG_CONFIG_LIBDIR=/dev/null
-        export PKG_CONFIG_LIBDIR
-    fi
-fi
-
 
 
 if test "$wxUSE_REGEX" != "no"; then

configure.in

@@ -2106,23 +2106,6 @@ fi
 dnl Find pkg-config outside of any conditional.  Done before any PKG_* call.
 PKG_PROG_PKG_CONFIG
 
-dnl When cross-compiling, don't use .pc files on the build system, they are at
-dnl best useless and can be harmful (e.g. they may define options inappropriate
-dnl for the cross-build, resulting in the failure of all the subsequent tests).
-if test "$build" != "$host"; then
-    dnl pkg.m4 forbids the use of PKG_XXX, so undo it here to avoid autoconf
-    dnl errors.
-    m4_pattern_allow([PKG_CONFIG_LIBDIR])
-
-    dnl If pkg-config libdir is already defined, we suppose that they know what
-    dnl they're doing and leave it alone, but if not, set it to a path in which
-    dnl no .pc files will be found.
-    if test -z "$PKG_CONFIG_LIBDIR"; then
-        PKG_CONFIG_LIBDIR=/dev/null
-        export PKG_CONFIG_LIBDIR
-    fi
-fi
-
 dnl ---------------------------------------------------------------------------
 dnl Optional libraries
 dnl