abs.3: wfix

Reported-by: Walter Harms <wharms@bfs.de>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>

man3/abs.3

@@ -121,6 +121,7 @@ to be declared, it may be necessary to define
 \fB_ISOC99_SOURCE\fP or \fB_ISOC9X_SOURCE\fP (depending on the
 version of glibc) before including any standard headers.
 .PP
+By default,
 GCC handles
 .BR abs (),
 .BR labs (),