[llvm] [libc] [libc][NFC] Move float macro into its own header / add target os detection (PR #73311)

[Clement Courbet via llvm-commits]

================
@@ -147,6 +147,8 @@ add_header_library(
     type_traits/true_type.h
     type_traits/type_identity.h
     type_traits/void_t.h
+  DEPENDS
+    libc.src.__support.macros.properties.float
----------------
legrosbuffle wrote:

This is missing a bunch of deps, you might want to add them too (in a separate patch)

https://github.com/llvm/llvm-project/pull/73311