Ports: Make sure HOST_* variables are set correctly for nested builds

When building a port as a dependency for another port the HOST_*
variables were previously initialized with values referring to the
SerenityOS toolchain.

Fixes SerenityOS#9168.

Ports/.port_include.sh

@@ -4,14 +4,16 @@ set -eu
 SCRIPT="$(dirname "${0}")"
 export SERENITY_ARCH="${SERENITY_ARCH:-i686}"
 
-HOST_CC="${CC:=cc}"
-HOST_CXX="${CXX:=c++}"
-HOST_AR="${AR:=ar}"
-HOST_RANLIB="${RANLIB:=ranlib}"
-HOST_PATH="${PATH:=}"
-HOST_PKG_CONFIG_DIR="${PKG_CONFIG_DIR:=}"
-HOST_PKG_CONFIG_SYSROOT_DIR="${PKG_CONFIG_SYSROOT_DIR:=}"
-HOST_PKG_CONFIG_LIBDIR="${PKG_CONFIG_LIBDIR:=}"
+if [ -z "${HOST_CC:=}" ]; then
+ export HOST_CC="${CC:=cc}"
+ export HOST_CXX="${CXX:=c++}"
+ export HOST_AR="${AR:=ar}"
+ export HOST_RANLIB="${RANLIB:=ranlib}"
+ export HOST_PATH="${PATH:=}"
+ export HOST_PKG_CONFIG_DIR="${PKG_CONFIG_DIR:=}"
+ export HOST_PKG_CONFIG_SYSROOT_DIR="${PKG_CONFIG_SYSROOT_DIR:=}"
+ export HOST_PKG_CONFIG_LIBDIR="${PKG_CONFIG_LIBDIR:=}"
+fi
 
 DESTDIR="/"