Configure: respecting user provided CFLAGS. #172

Job	Run time
buildbot / check-if-allowed	2s
buildbot / ubuntu-22.04, amd64, asan, quickjs-ng	9m 7s
buildbot / ubuntu-22.04, amd64, asan, njs	3m 9s
buildbot / ubuntu-22.04, amd64, asan, quickjs	9m 10s
buildbot / ubuntu-22.04, amd64, msan	5m 35s
buildbot / debian-12, amd64, print	1m 37s
buildbot / rhel-9, arm64	17m 30s
buildbot / amazonlinux-2, amd64	7m 24s
buildbot / alpine-3.20, amd64	12m 18s
buildbot / ubuntu-24.04, arm64	15m 15s
buildbot / debian-13, amd64	9m 13s
buildbot / alpine-3.22, amd64	12m 8s
buildbot / alpine-3.19, arm64	8m 47s
buildbot / freebsd-14, amd64	8m 39s
buildbot / debian-12, amd64	10m 36s
buildbot / alpine-3.21, amd64	12m 0s
buildbot / debian-11, amd64	8m 27s
buildbot / debian-11, arm64	6m 45s
buildbot / rhel-9, amd64	21m 13s
buildbot / rhel-10, amd64	20m 1s
buildbot / sles-15, amd64	18m 57s
buildbot / ubuntu-25.04, amd64	20m 5s
buildbot / rhel-8, arm64	6m 20s
buildbot / ubuntu-22.04, amd64	16m 45s
buildbot / rhel-8, amd64	8m 54s
buildbot / amazonlinux-2023, amd64	21m 26s
buildbot / ubuntu-22.04, arm64	13m 40s
buildbot / debian-12, x86	11m 8s
buildbot / ubuntu-24.04, amd64	17m 59s
buildbot / alpine-3.19, amd64	12m 8s
buildbot / amazonlinux-2023, arm64	17m 45s
	6h 4m 3s

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