sys-cluster/lmod: fix on prefix

Build system has CPPFLAGS="-I $TCL_INCLUDE", which breaks if the
TCL_INCLUDE returned by pkg-config is empty. However, this only
affects prefix.

Package-Manager: Portage-3.0.20, Repoman-3.0.3
Signed-off-by: Guilherme Amadio <amadio@gentoo.org>

sys-cluster/lmod/lmod-8.5.3.ebuild

@@ -95,6 +95,8 @@ src_configure() {
 		$(use_with cache cachedLoads)
 		$(use_with duplicate-paths duplicatePaths)
 		$(use_with auto-swap autoSwap)
+		# needed because configure.ac relies on TCL_INCLUDE not being empty
+		PKG_CONFIG_ALLOW_SYSTEM_CFLAGS=1
 	)
 	econf "${myconf[@]}"
 }