xca: work around make_install_args problem

I do not know why
${make_cmd} DESTDIR=${DESTDIR} ${make_install_args} ${make_install_target}
does not respect the setting of make_install_args, unless it happens that
"${DESTDIR}" is blank at template parse. Might be an xbps-src problem.
Regardless, this does the job.

Closes #6541 by actually installing the package files.

srcpkgs/xca/template

@@ -1,10 +1,9 @@
 # Template file for 'xca'
 pkgname=xca
 version=1.3.2
-revision=1
+revision=2
 build_style=gnu-configure
 make_build_target="all"
-make_install_args="destdir=${DESTDIR}"
 hostmakedepends="pkg-config qt5-tools qt5-host-tools"
 makedepends="qt5-devel libressl-devel libltdl-devel"
 short_desc="X Certificate and Key Management"
@@ -14,6 +13,10 @@ homepage="http://xca.sourceforge.net/"
 distfiles="${SOURCEFORGE_SITE}/${pkgname}/${version}/${pkgname}-${version}.tar.gz"
 checksum=04f11f2148c8369c1a1b4e109956ed8cc807ec266d0d936410624ba8ee4b5ce4
 
+pre_install() {
+	export destdir="${DESTDIR}"
+}
+
 post_install() {
 	vlicense COPYRIGHT
 }