[libc] [llvm] [libc][math][c23] Add {,u}fromfp{,x}{,f,l,f128} functions (PR #86003)

[via llvm-commits]

================
@@ -839,6 +839,198 @@ add_fp_unittest(
     libc.src.math.frexpf128
 )
 
+add_fp_unittest(
+  fromfp_test
+  SUITE
+    libc-math-smoke-tests
+  SRCS
+    fromfp_test.cpp
+  HDRS
+    FromfpTest.h
+  DEPENDS
+    libc.src.math.fromfp
----------------
overmighty wrote:

Right, but the `nextup` and `nextdown` tests only directly use `libc.src.math.{nextup,nextdown}` and test/UnitTest/{FPMatcher.h,Test.h}, and `add_fp_unittest` already takes care of the latter.

https://github.com/llvm/llvm-project/pull/86003