Setting __FLT_EVAL_METHOD__ to -1 with fast-math will set
__GLIBC_FLT_EVAL_METHOD to 2 and long double ends up being used for
float_t and double_t. This creates some ABI breakage with various C libraries.
See details here: https://github.com/llvm/llvm-project/issues/60781
This reverts commit bbf0d1932a3c1be970ed8a580e51edf571b80fd5.
When running `clang -E -Ofast` on macOS, the `__FLT_EVAL_METHOD__` macro is `0`, which causes the following typedef to be emitted into the preprocessed source: `typedef float float_t`.
However, when running `clang -c -Ofast`, `__FLT_EVAL_METHOD__` is `-1`, and `typedef long double float_t` is emitted.
This causes build errors for certain projects, which are not reproducible when compiling from preprocessed source.
The issue is that `__FLT_EVAL_METHOD__` is configured in `Sema::Sema` which is not executed when running in `-E` mode.
This change moves that logic into the preprocessor initialization method, which is invoked correctly in `-E` mode.
rdar://96134605
rdar://92748429
Differential Revision: https://reviews.llvm.org/D128814
