feat: add CFLAGS support

lfs/gcc-14.2.0.PKGBUILD

@@ -17,9 +17,7 @@ src_prepare() {
 }
 
 src_build() {
-  old_cflags="$CFLAGS"
-  unset CFLAGS
-
+  leaf_clear_flags
   mkdir -v build
   pushd build > /dev/null
   ../configure --prefix=/usr            \
@@ -33,8 +31,6 @@ src_build() {
                --disable-fixincludes    \
                --with-system-zlib
   make
-
-  export CFLAGS="$old_cflags"
   popd
 }
 
@@ -48,7 +44,7 @@ src_check() {
       -e '/GOTPCREL/d'              -i ../gcc/testsuite/gcc.target/i386/fentryname3.c
 
   chown -R leaf .
-  env -u CFLAGS su leaf -c "PATH=$PATH make -k check"
+  su leaf -c "PATH=$PATH make -k check"
   ../contrib/test_summary | grep -A7 Summ
   popd
 }