[docs] Fix documentation of -fno-strict-float-cast-overflow after D115804.

Previously this was documented as having the behavior of the
"target's native float-to-int conversion". After D115804, clang
uses saturating FP cast intrinsics which have the same behavior
on all targets.

Reviewed By: nikic

Differential Revision: https://reviews.llvm.org/D116856

clang/docs/ReleaseNotes.rst

@@ -243,6 +243,9 @@ Floating Point Support in Clang
   -ffp-contract=fast, whereas the (now corrected) default behavior is
   -ffp-contract=on.
   -ffp-model=precise is now exactly the default mode of the compiler.
+- -fstrict-float-cast-overflow no longer has target specific behavior. Clang
+  will saturate towards the smallest and largest representable integer values.
+  NaNs will be converted to zero.
 
 Internal API Changes
 --------------------

clang/docs/UsersManual.rst

@@ -1380,8 +1380,8 @@ floating point semantic models: precise (the default), strict, and fast.
    When a floating-point value is not representable in a destination integer
    type, the code has undefined behavior according to the language standard.
    By default, Clang will not guarantee any particular result in that case.
-   With the 'no-strict' option, Clang attempts to match the overflowing behavior
-   of the target's native float-to-int conversion instructions.
+   With the 'no-strict' option, Clang will saturate towards the smallest and
+   largest representable integer values instead. NaNs will be converted to zero.
 
 .. _opt_fmath-errno: