configure: fix oss fuzz build
configure: fix oss fuzz build

When fuzzing is enabled we enforce clang and check if $CC == "clang".
That was fine before, but now the OSS fuzz compiler is called
/src/aflplusplus/afl-clang-fast.

Fixes: #2005
Signed-off-by: Tadeusz Struk <ac7da5bc34fbda078ba4af5ef710d2a59a2316f5@intel.com>

tpm2-software/tpm2-tss,01org/tpm2-tss,01org/TPM2.0-TSS,tpm2-software/tpm2-tss,01org/tpm2-tss,01org/TPM2.0-TSS,01org/TPM2.0-TSS,01org/tpm2-tss,tpm2-software/tpm2-tss,01org/TPM2.0-TSS