Try using LIBRARY_PATH to catch built libs (#88)

* Revert "Revert "[osx_steps] export cppflags""

This reverts commit 7956064f.

* Try using LIBRARY_PATH instead of LDFLAGS

tests/test_library_builders.sh

@@ -11,7 +11,7 @@ if [ "$TRAVIS_OS_NAME" == "osx" ]; then brew update; fi
 start_spinner
 
 suppress build_openssl
-suppress build_openblas
+suppress build_libpng
 suppress build_libwebp
 suppress build_szip
 suppress build_swig

travis_steps.sh

@@ -10,3 +10,7 @@ if [[ "$TRAVIS_OS_NAME" == "osx" ]]; then
 else
     source $MULTIBUILD_DIR/travis_linux_steps.sh
 fi
+
+# Promote BUILD_PREFIX on search path to any newly built libs
+export CPPFLAGS="-L$BUILD_PREFIX/include $CPPFLAGS"
+export LIBRARY_PATH="$BUILD_PREFIX/lib:$LIBRARY_PATH"