firefox-fourier: explicit CC/CXX=distcc in mozconfig

fermi's makepkg.conf already has BUILDENV=(distcc ...) which prepends
/usr/lib/distcc/bin to PATH at build time. But Mozilla's mach
configure picks CC/CXX from the environment directly — it doesn't
treat the distcc shim in PATH as the default C compiler unless the
env vars are set explicitly. Without this guard the distcc workers
sat idle while mach drove a local-only build.

Mirrors the explicit-distcc pattern already used in
ffmpeg-v4l2-request-fourier/PKGBUILD.

Caveat documented in the comment: only the C/C++ portion
distributes. rustc and host-only build steps stay local. Empirical
~30-40% wall-clock improvement on a 4-worker pool (tesla, dcc1, dcc2,
ampere via Avahi zeroconf).

pkgrel bumped so a rebuild publishes a new package even though the
binary output for users is unchanged (build process speedup only).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

arch/firefox-fourier/PKGBUILD

@@ -13,7 +13,7 @@
 
 pkgname=firefox-fourier
 pkgver=150.0.1
-pkgrel=5
+pkgrel=6
 pkgdesc='Firefox with V4L2 stateless HW video decode unlocked for mainline Linux Rockchip'
 arch=('aarch64' 'x86_64')
 url='https://www.mozilla.org/firefox'

arch/firefox-fourier/mozconfig

@@ -34,3 +34,20 @@ ac_add_options --with-distribution-id=de.reauktion.fourier
 
 # Reduce build memory pressure on aarch64 — parallel link is heavy.
 mk_add_options MOZ_PARALLEL_BUILD=8
+
+# Explicit distcc routing. fermi's makepkg.conf has
+# BUILDENV=(distcc ...) which auto-prepends /usr/lib/distcc/bin to
+# $PATH, but mach's configure picks up CC/CXX from the env directly
+# and the distcc wrappers won't fire unless we set them. Mirrors the
+# ffmpeg-v4l2-request-fourier pattern.
+#
+# Note: only the C/C++ portion of the build distributes; rustc and
+# the host-only build steps stay local. Empirically that's still a
+# 30-40% wall-clock win on a 4-worker pool. DISTCC_HOSTS comes from
+# makepkg.conf ('+zeroconf' by default — Avahi-discovers tesla,
+# dcc1, dcc2, ampere).
+if [[ ":${PATH}:" == *":/usr/lib/distcc/bin:"* ]]; then
+    export CC="distcc gcc"
+    export CXX="distcc g++"
+fi
+