[PATCH v2 1/2] man/man2/adjtimex.2: Add include and macro for clock_adjtime

[Georg Sauthoff <mail@gms.tf>]

GNU libc declares clock_adjtime() when including time.h, and not when
just sys/timex.h is included, iff support for GNU features is requested.

Verification:

    $ for i in BLAH _GNU_SOURCE; do for j in sys/timex.h time.h; do echo -n "Testing $i and $j ... "; echo -e '#define '"$i"'\n#include <'"$j"'>\nvoid f(){clock_adjtime;}' | gcc  -xc - -o /dev/null -c 2>/dev/null && echo OK || echo FAIL; done; done
    Testing BLAH and sys/timex.h ... FAIL
    Testing BLAH and time.h ... FAIL
    Testing _GNU_SOURCE and sys/timex.h ... FAIL
    Testing _GNU_SOURCE and time.h ... OK

(Test output is from a Fedora 43 system)

Signed-off-by: Georg Sauthoff <mail@gms.tf>
---
 man/man2/adjtimex.2 | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/man/man2/adjtimex.2 b/man/man2/adjtimex.2
index f12d9413e..5b9a0667b 100644
--- a/man/man2/adjtimex.2
+++ b/man/man2/adjtimex.2
@@ -17,9 +17,12 @@ .SH SYNOPSIS
 .P
 .BI "int adjtimex(struct timex *" "buf" );
 .P
-.BI "int clock_adjtime(clockid_t " clk_id, " struct timex *" "buf" );
-.P
 .BI "int ntp_adjtime(struct timex *" buf );
+.P
+.BR #define\~_GNU_SOURCE "  // See feature_test_macros(7)"
+.B #include <time.h>
+.P
+.BI "int clock_adjtime(clockid_t " clk_id, " struct timex *" "buf" );
 .fi
 .SH DESCRIPTION
 Linux uses David L.\& Mills' clock adjustment algorithm (see RFC\ 5905).
-- 
2.55.0