Description:
------------
While running configure on macOS, the system library path is getting added to the list of library paths via the autoconf function PHP_ADD_LIBPATH. The build tools on macOS use paths like "/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.13.sdk/usr/lib" and "/Library/Developer/CommandLineTools/SDKs/MacOSX10.13.sdk/usr/lib" that the linker knows to refer back to the more common /usr/lib.

This is causing the macOS linker to link to system libraries rather than versions explicitly provided in configure flags.

This issue is affecting the Homebrew package manager, tracked at https://github.com/Homebrew/homebrew-core/issues/28398

Test script:
---------------
./configure
--prefix=/usr/local/Cellar/php/7.2.6
--localstatedir=/usr/local/var
--sysconfdir=/usr/local/etc/php/7.2
--with-config-file-path=/usr/local/etc/php/7.2
--with-config-file-scan-dir=/usr/local/etc/php/7.2/conf.d
--with-pear=/usr/local/Cellar/php/7.2.6/share/php/pear
--enable-bcmath
--enable-calendar
--enable-dba
--enable-dtrace
--enable-exif
--enable-ftp
--enable-fpm
--enable-intl
--enable-mbregex
--enable-mbstring
--enable-mysqlnd
--enable-opcache-file
--enable-pcntl
--enable-phpdbg
--enable-phpdbg-webhelper
--enable-shmop
--enable-soap
--enable-sockets
--enable-sysvmsg
--enable-sysvsem
--enable-sysvshm
--enable-wddx
--enable-zip
--with-apxs2=/usr/local/opt/httpd/bin/apxs
--with-bz2
--with-fpm-user=_www
--with-fpm-group=_www
--with-freetype-dir=/usr/local/opt/freetype
--with-gd
--with-gettext=/usr/local/opt/gettext
--with-gmp=/usr/local/opt/gmp
--with-icu-dir=/usr/local/opt/icu4c
--with-jpeg-dir=/usr/local/opt/jpeg
--with-kerberos
--with-layout=GNU
--with-ldap
--with-ldap-sasl
--with-libedit
--with-libzip
--with-mhash
--with-mysql-sock=/tmp/mysql.sock
--with-mysqli=mysqlnd
--with-ndbm
--with-openssl=/usr/local/opt/openssl
--with-password-argon2=/usr/local/opt/argon2
--with-pdo-dblib=/usr/local/opt/freetds
--with-pdo-mysql=mysqlnd
--with-pdo-odbc=unixODBC,/usr/local/opt/unixodbc
--with-pdo-pgsql=/usr/local/opt/libpq
--with-pgsql=/usr/local/opt/libpq
--with-pic
--with-png-dir=/usr/local/opt/libpng
--with-pspell=/usr/local/opt/aspell
--with-sodium=/usr/local/opt/libsodium
--with-unixODBC=/usr/local/opt/unixodbc
--with-webp-dir=/usr/local/opt/webp
--with-xmlrpc
--with-xsl
--with-zlib
--with-curl

Expected result:
----------------
The php binary is compiled and linked to the libpq library at /usr/local/opt/libpq/lib/libpq.5.dylib.

The Makefile does not include references to macOS's build tool SDK directories.

Actual result:
--------------
The php binary is compiled and linked to the system libpq library at /usr/lib/libpq.5.dylib.

The Makefile includes references to /Library/Developer/CommandLineTools/SDKs/MacOSX10.13.sdk/usr/lib.