build: add -Wall

I noticed that unused variables are not complained about by the build. Let's
add -Wall.

I also noticed that the Makefile.ams include STD_DEFINES_AND_INCLUDES, which is
never set in configure.ac, so using that to add -Wall to all build contexts.

Change-Id: I16711cf5a1ef8bd611074b3dd486ed7a0ae9df64
1 file changed