Handle global symbols in code segment.

[andreistefanescu]

The verification of gcm_init_avx, gcm_gmult_avx, gcm_ghash_avx, aesni_gcm_encrypt, and aesni_gcm_decrypt requires global symbols L0x1c2_polynomial and .Lbswap_mask, which are part of the code segment, and thus have relative addresses rather than absolute addresses. This is handled by adding gcm_ghash_avx and aesni_gcm_encrypt to the list of global symbols for the verification command, with sizes large enough to ensure that the required global symbols are in scope. This should be handled in a more principled way.