travis: fix a typo and create bogus directories to avoid compiler warnings

(back-ported from commit 46710ba)

Author: ggouaillardet

.travis.yml

@@ -40,7 +40,7 @@ env:
     global:
         - AM_MAKEFLAGS="-j4"
         - CPPFLAGS="-I$HOME/bogus/include"
-        - LDFLAGS="-I$HOME/bogus/lib"
+        - LDFLAGS="-L$HOME/bogus/lib"
         - LD_LIBRARY_PATH="$HOME/bogus/lib"
     matrix:
         - GCC_VERSION=default