chroot-git: keep build flag consistent in all stage

git build system will trigger a rebuild if it detects
if flags passed to make changed.

In commit 886036d094, ("chroot-git: correct iconv usage on musl",
2019-10-30), we tried to correct the git-iconv interaction on musl,
but we forget to pass that flag into `make install'.

Hence, on do_install, git build system rebuild git without
ICONV_OMITS_BOM=Yes flag, thus produce faulty binary.

Save that flag into config.mak[1] in order to keep it consistent across
build stage.

While we're at it, also move other make_*_args into config.mak

[1]: https://public-inbox.org/git/20191031181116.GC2133@sigill.intra.peff.net/

srcpkgs/chroot-git/template

@@ -1,7 +1,7 @@
 # Template file for 'chroot-git'
 pkgname=chroot-git
 version=2.23.0
-revision=2
+revision=3
 bootstrap=yes
 wrksrc="git-${version}"
 build_style=gnu-configure
@@ -9,8 +9,6 @@ configure_args="--without-curl --without-openssl
  --without-python --without-expat --without-tcltk
  ac_cv_lib_curl_curl_global_init=no ac_cv_lib_expat_XML_ParserCreate=no
  ac_cv_snprintf_returns_bogus=no"
-make_build_args="CC_LD_DYNPATH=-L"
-make_install_args="NO_INSTALL_HARDLINKS=1"
 makedepends="zlib-devel"
 short_desc="GIT Tree History Storage Tool -- for xbps-src use"
 maintainer="Enno Boland <gottox@voidlinux.org>"
@@ -28,11 +26,20 @@ fi
 case "$XBPS_TARGET_MACHINE" in
 	*-musl)
 		configure_args+=" ac_cv_fread_reads_directories=yes"
-		make_build_args+=" ICONV_OMITS_BOM=Yes"
 		;;
 	*) configure_args+=" ac_cv_fread_reads_directories=no" ;;
 esac
 
+post_configure() {
+	cat <<-EOF >config.mak
+	CC_LD_DYNPATH=-L
+	NO_INSTALL_HARDLINKS=Yes
+	EOF
+	case "$XBPS_TARGET_MACHINE" in
+		*-musl) echo "ICONV_OMITS_BOM=Yes" >>config.mak ;;
+	esac
+}
+
 do_install() {
 	# remove unneeded stuff.
 	make DESTDIR=${wrksrc}/build-tmp install