devicepkg-dev: opt-out compiler-gcc.h replacing

Instead of never overwriting compiler-gcc.h if it exists, overwrite it by default except if OVERWRITE_GCCH=0 is set in the environment.

Most kernels do need this file replaced and won't build without this patch anymore (see ff25ad7a).

main/devicepkg-dev/APKBUILD

 pkgname="devicepkg-dev"
-pkgver=0.7
+pkgver=0.8
 pkgrel=0
 pkgdesc="Provides default device package functions"
 url="https://postmarketos.org"
@@ -59,7 +59,7 @@ package() {
 sha512sums="d69930dd790b00fb39760a37d95a10899f0d167e10e2804feb05d9ce04f94185dc32d36edc90214aba2ea2aa09bf18f7dab93f1d2eff23f67beb2cc83be30e7c  compiler-gcc.h
 55943344e6c6192642f20246566c8468dba33d4ec4223c4e930f723fdb0fa248001c65a9bbaa5f15c18e9a42811c9b9decedfd5586f481aa762b6423b55d55bb  devicepkg_build.sh
 cc35989539781da2bc847fe68448863174a79db3853f836c61da064030cb729a16681cb6ffa16add558a7dba8563cb7fab495a6db811dcc3a1af5123dc0e6f72  devicepkg_package.sh
-786673de073988aff5a4c5a4a3da07131dc693970f5492a99816e8b20caf2cd67365ed9398f74f0f0e9a0a3b5759220b9d5d79d77164357ed823ab44f364c8bc  downstreamkernel_prepare.sh
+1b038d0bca1e130674497cf7aeb26fac2bcec510ce094fa6f6700fcdcabc778741541c1aa89d3588ed42908f60708a2d9b83ffd5e50e99db619d366458e82256  downstreamkernel_prepare.sh
 bedf319a74bff01780192cd11c872c41a451915cc7e7542c467cd84fa1784236401f57e197258c3aae734f478c31a2052129838861ea204c0985630501f152ca  devicepkg_subpackage_kernel.sh
 9bb7f2a0930f397a713e9f4b6d5b83a426d9a2a3f692dcc42ac30717bf26ead869d8823a38f3ad388af12b2b9a02e8ec4d4418e9c2062389ed06d2b891a49ff3  deviceinfo
 136247a16ec91dc0c7241eeddb28c2196ae3b29946a9bc7e9566f848491ef1c53b12d05bf2dbc1cc352986712fd76f25c1510bcc8f301af540a2f01c33b299e1  expected-deviceinfo-downstream