[gcc r13-6513] doc: Document testsuite check_effective_target_tail_call

[Hans-Peter Nilsson]

https://gcc.gnu.org/g:318c9101a3bc24e4cd1a89eeb52531988a11c89f

commit r13-6513-g318c9101a3bc24e4cd1a89eeb52531988a11c89f
Author: Hans-Peter Nilsson <hp@axis.com>
Date:   Fri Mar 3 21:21:29 2023 +0100

    doc: Document testsuite check_effective_target_tail_call
    
    Spot-checked the PDF output for sanity.
    
            * doc/sourcebuild.texi: Document check_effective_target_tail_call.

Diff:
---
 gcc/doc/sourcebuild.texi | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/gcc/doc/sourcebuild.texi b/gcc/doc/sourcebuild.texi
index c348a1e47cc..80bef7f0a0e 100644
--- a/gcc/doc/sourcebuild.texi
+++ b/gcc/doc/sourcebuild.texi
@@ -2844,6 +2844,9 @@ Target supports named sections.
 Target uses natural alignment (aligned to type size) for types of
 32 bits or less.
 
+@item tail_call
+Target supports tail-call optimizations.
+
 @item target_natural_alignment_64
 Target uses natural alignment (aligned to type size) for types of
 64 bits or less.