Test all <build attribute, value> pairs.

Add more tests to make sure the encoding/decoding of build attributes works
correctly for all permissible values of build attributes. For cases where there
are an infinite number of such values, a representative subset has been settled
for.

Change-Id: I2643c9624c211b2d56405306e16eec2d487bc5d6
llvm-svn: 222917