Elfutils: Don't warn on seemingly unused variable

When asserts are nops, the compiler thinks the variable is unused
and will issue a terminal warning.

Locally turning off the warning is preferred as it eases upgrading
the project.

Change-Id: I2a910b02bc2ebd2ec299fee0426aea1390eaf9d4
Merge "Elfutils: Don't warn on seemingly unused variable"