Don't install one-line "helper header" cblas.h into /usr/include,
as it conflicts with sci-libs/lapack.
--- a/Makefile
+++ b/Makefile
@@ -1052,7 +1052,7 @@ endif
 
 # --- Install header rules ---
 
-install-headers: check-env $(MK_INCL_DIR_INST) install-helper-headers
+install-headers: check-env $(MK_INCL_DIR_INST)
 
 # Rule for installing main headers.
 $(MK_INCL_DIR_INST): $(HEADERS_TO_INSTALL) $(CONFIG_MK_FILE)