autoconf: require C99

4 jobs for master in 1 minute and 5 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Build
passed #426369
amd64 docker
build-debian

00:00:29

passed #426370
macos
build-macos

00:00:57

passed #426372
amd64 docker
build-win32

00:01:05

passed #426371
amd64 docker
build-win64

00:01:05