fix compile for Clang

[geekLucian]

When trying to compile riscv-tests with clang, several incompatible compilation issues between clang and gcc are met, such as:

• https://github.com/riscv-software-src/riscv-tests/pull/225
• clang doesn't support immediates like 0f:7fc00000
• clang doesn't support bf16 until https://github.com/llvm/llvm-project/commit/e4888a37d36780872d685c68ef8b26b2e14d6d39, but it only works for X86 yet, and will not affect current release of clang (i.e. clang-14)
• GNU as let .weak override .globl, while clang lets the last directive win https://reviews.llvm.org/D90108