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 82a5337c07, ("git: correct utf-16 and utf-32 conversion 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/git/template

@@ -1,12 +1,10 @@
 # Template file for 'git'
 pkgname=git
 version=2.23.0
-revision=2
+revision=3
 build_style=gnu-configure
 configure_args="--with-curl --with-expat --with-tcltk --with-libpcre2
  ac_cv_snprintf_returns_bogus=no"
-make_install_args="NO_INSTALL_HARDLINKS=1 INSTALLDIRS=vendor
- perllibdir=/usr/share/perl5/vendor_perl"
 make_check_target=test
 hostmakedepends="asciidoc perl pkg-config tk xmlto"
 makedepends="libglib-devel libcurl-devel libsecret-devel pcre2-devel tk-devel"
@@ -27,11 +25,21 @@ subpackages="git-cvs git-svn gitk git-gui git-all git-libsecret"
 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
+	NO_INSTALL_HARDLINKS=Yes
+	INSTALLDIRS=vendor
+	perllibdir=/usr/share/perl5/vendor_perl
+	EOF
+	case "$XBPS_TARGET_MACHINE" in
+		*-musl) echo "ICONV_OMITS_BOM=Yes" >>config.mak ;;
+	esac
+}
+
 post_build() {
 	make ${makejobs} -C Documentation man
 	make ${makejobs} -C contrib/contacts all git-contacts.1