build: define _GNU_SOURCE only on the command line

Not in source files

See https://ariadne.space/2021/12/21/stop-defining-feature-test-macros-in-your-code/

Signed-off-by: Steve Bennett <steveb@workware.net.au>

1 files changed, 2 insertions, 0 deletions

diff --git a/auto.def b/auto.def
index e9d6002..36ab1e3 100644
--- a/auto.def
+++ b/auto.def
@@ -209,6 +209,8 @@ cc-check-sizeof int
 # Default optimisation
 define-append AS_CPPFLAGS -O2
 
+define-append AS_CPPFLAGS -D_GNU_SOURCE
+
 # check, but don't add to -cflags
 cc-with {} {
     cc-check-flags -fno-unwind-tables -fno-asynchronous-unwind-tables