git: 6fc164c7775a - main - cdefs.9: Note only one programming environment at a time

The branch main has been updated by imp:

URL: https://cgit.FreeBSD.org/src/commit/?id=6fc164c7775a5dc7a4277969870abd50eb62cd1e

commit 6fc164c7775a5dc7a4277969870abd50eb62cd1e
Author:     Warner Losh <imp@FreeBSD.org>
AuthorDate: 2025-01-06 23:45:47 +0000
Commit:     Warner Losh <imp@FreeBSD.org>
CommitDate: 2025-01-06 23:46:06 +0000

    cdefs.9: Note only one programming environment at a time
    
    Only one programming environment at a time can be defined at a
    time. Posix states that when defining _POSIX_C_SOURCE, the system
    headers must define only the macros, variables, and functions that a
    given standard level defines. Selecting a different macro along with
    this is fundamentally incompatible with that.
    
    Sponsored by:           Netflix
---
 share/man/man9/cdefs.9 | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/share/man/man9/cdefs.9 b/share/man/man9/cdefs.9
index b9821c70f2a1..2e6f1b440efb 100644
--- a/share/man/man9/cdefs.9
+++ b/share/man/man9/cdefs.9
@@ -3,7 +3,7 @@
 .\"
 .\" SPDX-License-Identifier: BSD-2-Clause
 .\"
-.Dd December 6, 2024
+.Dd January 6, 2025
 .Dt CDEFS 9
 .Os
 .Sh NAME
@@ -352,6 +352,7 @@ Defining the macros outlined below requests that the system header files provide
 only the functions, structures and macros (symbols) defined by the appropriate
 standard, while suppressing all extensions.
 However, system headers not defined by that standard may define extensions.
+You may only define one of the following for any compilation unit.
 .Bl -column "---------------"
 .It Sy Macro Ta Sy Environment
 .It Dv _POSIX_SOURCE Ta St -p1003.1-88 including St -ansiC