[glib] build: fix 'make distclean'

[Ryan Lortie <desrt src gnome org>]

commit 028856a99fd8ce7dc6a1318a6b57cdbbefbc6bdc
Author: Ryan Lortie <desrt desrt ca>
Date:   Mon Jan 13 16:41:31 2014 -0500

    build: fix 'make distclean'
    
    Don't run a non-existent lcov command to clean up during 'make distclean'

 glib.mk |    4 +++-
 1 files changed, 3 insertions(+), 1 deletions(-)
---
diff --git a/glib.mk b/glib.mk
index 00f2e42..09aae0e 100644
--- a/glib.mk
+++ b/glib.mk
@@ -59,7 +59,9 @@ genlcov:
        @echo "file://$(abs_top_builddir)/glib-lcov/index.html"
 
 lcov-clean:
-       $(AM_V_GEN) $(LTP) --quiet --directory $(top_builddir) -z
+       if test -n "$(LTP)"; then \
+         $(LTP) --quiet --directory $(top_builddir) -z; \
+       fi
 
 # run tests in cwd as part of make check
 check-local: test-nonrecursive