[libc] [llvm] [libc] Add proxy headers for fenv types. (PR #88467)

[Nick Desaulniers via llvm-commits]

================
@@ -41,6 +41,24 @@ add_proxy_header_library(
     libc.include.fenv
 )
 
+add_proxy_header_library(
+  fenv_t
----------------
nickdesaulniers wrote:

types should go in libc/hdrs/types/

https://github.com/llvm/llvm-project/pull/88467