[gcc r13-3002] Document -fexcess-precision=16 in target.def

[H.J. Lu]

https://gcc.gnu.org/g:2002c54cb7f183c27ad7a5c294b868930cea17db

commit r13-3002-g2002c54cb7f183c27ad7a5c294b868930cea17db
Author: H.J. Lu <hjl.tools@gmail.com>
Date:   Fri Sep 30 15:51:18 2022 -0700

    Document -fexcess-precision=16 in target.def
    
            * target.def (TARGET_C_EXCESS_PRECISION): Document
            -fexcess-precision=16.

Diff:
---
 gcc/target.def | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/gcc/target.def b/gcc/target.def
index 4d49ffc2c88..a3d3b04a165 100644
--- a/gcc/target.def
+++ b/gcc/target.def
@@ -6181,7 +6181,7 @@ of the excess precision explicitly added.  For\n\
 @code{EXCESS_PRECISION_TYPE_FLOAT16}, and\n\
 @code{EXCESS_PRECISION_TYPE_FAST}, the target should return the\n\
 explicit excess precision that should be added depending on the\n\
-value set for @option{-fexcess-precision=@r{[}standard@r{|}fast@r{]}}.\n\
+value set for @option{-fexcess-precision=@r{[}standard@r{|}fast@r{|}16@r{]}}.\n\
 Note that unpredictable explicit excess precision does not make sense,\n\
 so a target should never return @code{FLT_EVAL_METHOD_UNPREDICTABLE}\n\
 when @var{type} is @code{EXCESS_PRECISION_TYPE_STANDARD},\n\