build (macos): do not overwrite PKG_CONFIG_PATH variable

Author: botantony

configure

@@ -13,7 +13,7 @@ ARCH=$(uname -m)
 if [ "$OS-$ARCH" = "Darwin-arm64" ]; then
 CPATH=/opt/homebrew/include
 LIBRARY_PATH=/opt/homebrew/lib
-export PKG_CONFIG_PATH=/opt/homebrew/opt/sqlite/lib/pkgconfig
+export PKG_CONFIG_PATH=${PKG_CONFIG_PATH}:/opt/homebrew/opt/sqlite/lib/pkgconfig
 else
 CPATH=/usr/local/lib
 LIBRARY_PATH=/usr/local/lib