math.h: Warn about an already-defined log macro

This is a common programming error, and the cause of the problem is not
always obvious.

<tgmath.h> defines a log macro, but it includes <math.h> before that, so
that is compatible with the warning.

1 files changed, 4 insertions, 0 deletions

diff --git a/ChangeLog b/ChangeLog
index ef4a6edc5e..a9fb242bf2 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+2017-09-04  Florian Weimer  <fweimer@redhat.com>
+
+	* math/math.h: Issue warning if log is defined.
+
 2017-09-04  Joseph Myers  <joseph@codesourcery.com>
 
 	* scripts/build-many-glibcs.py (Context.checkout): Default Linux