configure: add pkg-config check for zlib

It exists, so why not use it? Helps one get rid of additional
search path related flags in addition to PKG_CONFIG_{PATH,LIBDIR}
when utilizing a cross-prefix separate from the sysroot.

diff --git a/configure b/configure
index f78853cc6c797c191e0184806db18cc06130569b..2d99c8ea8571e9a8083f30eae7f9b1ce863ca43d 100755 (executable)
--- a/configure
+++ b/configure
@@ -5933,7 +5933,8 @@ if ! disabled pthreads && ! enabled w32threads && ! enabled os2threads; then
     fi
 fi
 
-enabled  zlib && check_lib zlib   zlib.h      zlibVersion    -lz
+enabled  zlib && { check_pkg_config zlib zlib "zlib.h" zlibVersion ||
+                   check_lib zlib   zlib.h      zlibVersion    -lz; }
 enabled bzlib && check_lib bzlib bzlib.h BZ2_bzlibVersion    -lbz2
 enabled  lzma && check_lib lzma   lzma.h lzma_version_number -llzma