Add include and lib dirs from libpq --cppflags, --ldflags

They seem the right thing to fix MacOS build woes.

Inspired to #935, might close #1200.

NEWS

@@ -12,6 +12,8 @@ What's new in psycopg 2.9
 - Connection exceptions with sqlstate ``08XXX`` reclassified as
   `~psycopg2.OperationalError` (a subclass of the previously used
   `~psycopg2.DatabaseError`) (:ticket:`#1148`).
+- Include library dirs required from libpq to work around MacOS build problems
+  (:ticket:`#1200`).
 
 
 What's new in psycopg 2.8.7

scripts/build/build_macos.sh

@@ -35,10 +35,6 @@ mkdir -p "$DISTDIR"
 # Install required python packages
 pip install -U pip wheel delocate
 
-# Allow to find the libraries needed.
-export LDFLAGS="-L/usr/local/opt/openssl@1.1/lib"
-export CPPFLAGS="-I/usr/local/opt/openssl@1.1/include"
-
 # Replace the package name
 gsed -i "s/^setup(name=\"psycopg2\"/setup(name=\"${PACKAGE_NAME}\"/" \
     "${PRJDIR}/setup.py"

setup.py

@@ -376,6 +376,16 @@ For further information please check the 'doc/src/install.rst' file (also at
             self.library_dirs.append(pg_config_helper.query("libdir"))
             self.include_dirs.append(pg_config_helper.query("includedir"))
             self.include_dirs.append(pg_config_helper.query("includedir-server"))
+
+            # add includedirs from cppflags, libdirs from ldflags
+            for token in pg_config_helper.query("ldflags").split():
+                if token.startswith("-L"):
+                    self.library_dirs.append(token[2:])
+
+            for token in pg_config_helper.query("cppflags").split():
+                if token.startswith("-I"):
+                    self.include_dirs.append(token[2:])
+
             pgversion = pg_config_helper.query("version").split()[1]
 
             verre = re.compile(