Prepend brew's pkgconfig to PKG_CONFIG_PATH

This is another attempt to fix recent macOS x64 configure failures.

Author: cmb69

.github/actions/configure-macos/action.yml

@@ -11,13 +11,13 @@ runs:
         set -x
         BREW_OPT="$(brew --prefix)"/opt
         export PATH="$BREW_OPT/bison/bin:$PATH"
-        export PKG_CONFIG_PATH="$PKG_CONFIG_PATH:$BREW_OPT/[email protected]/lib/pkgconfig"
-        export PKG_CONFIG_PATH="$PKG_CONFIG_PATH:$BREW_OPT/curl/lib/pkgconfig"
-        export PKG_CONFIG_PATH="$PKG_CONFIG_PATH:$BREW_OPT/libffi/lib/pkgconfig"
-        export PKG_CONFIG_PATH="$PKG_CONFIG_PATH:$BREW_OPT/libxml2/lib/pkgconfig"
-        export PKG_CONFIG_PATH="$PKG_CONFIG_PATH:$BREW_OPT/libxslt/lib/pkgconfig"
-        export PKG_CONFIG_PATH="$PKG_CONFIG_PATH:$BREW_OPT/zlib/lib/pkgconfig"
-        export PKG_CONFIG_PATH="$PKG_CONFIG_PATH:$BREW_OPT/icu4c/lib/pkgconfig"
+        export PKG_CONFIG_PATH="$BREW_OPT/[email protected]/lib/pkgconfig:$PKG_CONFIG_PATH"
+        export PKG_CONFIG_PATH="$BREW_OPT/curl/lib/pkgconfig:$PKG_CONFIG_PATH"
+        export PKG_CONFIG_PATH="$BREW_OPT/libffi/lib/pkgconfig:$PKG_CONFIG_PATH"
+        export PKG_CONFIG_PATH="$BREW_OPT/libxml2/lib/pkgconfig:$PKG_CONFIG_PATH"
+        export PKG_CONFIG_PATH="$BREW_OPT/libxslt/lib/pkgconfig:$PKG_CONFIG_PATH"
+        export PKG_CONFIG_PATH="$BREW_OPT/zlib/lib/pkgconfig:$PKG_CONFIG_PATH"
+        export PKG_CONFIG_PATH="$BREW_OPT/icu4c/lib/pkgconfig:$PKG_CONFIG_PATH"
         ./buildconf --force
         ./configure \
           --enable-option-checking=fatal \