git: cfd8866818ab - main - cdefs.h: Add warning about defining __BSD_VISIBLE and friends

The branch main has been updated by imp:

URL: https://cgit.FreeBSD.org/src/commit/?id=cfd8866818abb68fbfbffb925298c0b457cb32b5

commit cfd8866818abb68fbfbffb925298c0b457cb32b5
Author:     Warner Losh <imp@FreeBSD.org>
AuthorDate: 2025-01-06 23:45:51 +0000
Commit:     Warner Losh <imp@FreeBSD.org>
CommitDate: 2025-01-06 23:46:06 +0000

    cdefs.h: Add warning about defining __BSD_VISIBLE and friends
    
    Undefined things happen if users define these macros, be more explicit
    about documenting 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 2e6f1b440efb..4efce132d393 100644
--- a/share/man/man9/cdefs.9
+++ b/share/man/man9/cdefs.9
@@ -401,7 +401,8 @@ are also included.
 These macros are set by
 .Nm
 to control the visibility of different standards.
-Users should not use these, but they are documented here for developers.
+Users must not define these, and doing so will produced undefined results.
+They are documented here for developers working on system's header files.
 .Bl -column "---------------"
 .It Dv __XSI_VISIBLE Ta Restricts the visibility of XOPEN Single Unix Standard version.
 Possible values are 500, 600, 700 or 800, corresponding to Issue 5, 6, 7, or 8