clang: add helper script to keep package updated

We'll need to update our clang when Msys2 updates theirs and reapply our
customisations every time, so a script makes this job less tedious and
leaves no room to miss a step of the process.
This script performs the same steps as the previous two commits. (it
was used to generate the files for those)

Signed-off-by: Matthias Aßhauer <mha1993@live.de>

mingw-w64-clang/update-clang-from-msys2.sh

@@ -0,0 +1,60 @@
+#!/usr/bin/bash
+die () {
+	printf "$@" >&2
+	cleanup
+	exit 1
+}
+cleanup(){
+	rm -rf upstream
+}
+
+pkgname=mingw-w64-clang
+
+old_pkgver="$(sed -ne 's/pkgver=\([.0-9]*\).*/\1/p' -e 's/_version=\([.0-9]*\).*/\1/p' < PKGBUILD)"
+old_pkgrel="$(sed -ne 's/pkgrel=\([0-9]*\).*/\1/p' < PKGBUILD)"
+
+test -n "$old_pkgver" ||
+	die "$0: could not determine current pkgver\n"
+
+test -n "$old_pkgrel" ||
+	die "$0: could not determine current pkgrel\n"
+
+git clone --sparse --depth 1 https://github.com/msys2/MINGW-packages upstream
+cd upstream
+git sparse-checkout add $pkgname
+cd ..
+
+new_pkgver="$(sed -ne 's/pkgver=\([.0-9]*\).*/\1/p' -e 's/_version=\([.0-9]*\).*/\1/p' < upstream/$pkgname/PKGBUILD)"
+new_pkgrel="$(sed -ne 's/pkgrel=\([0-9]*\).*/\1/p' < upstream/$pkgname/PKGBUILD)"
+rc="$(sed -ne 's/_rc="\(*\)".*/\1/p' < upstream/$pkgname/PKGBUILD)"
+
+test -n "$new_pkgver" ||
+	die "$0: could not determine new pkgver\n"
+
+test -n "$new_pkgrel" ||
+	die "$0: could not determine new pkgrel\n"
+
+test -z "$rc" ||
+    die "$0: MSYS2 is currently on an RC version. This script is not able to handle RC versions."
+
+test "$new_pkgver" = "$old_pkgver" &&
+    new_pkgrel="$old_pkgrel"
+
+new_pkgrel=$(("$new_pkgrel"+1))
+
+rm -f *.patch
+mv upstream/$pkgname/*.patch ./
+rm -f PKGBUILD
+mv upstream/$pkgname/PKGBUILD ./
+rm -f README-patches.md
+mv upstream/$pkgname/README-patches.md ./
+
+sed -i "s/pkgrel=[.0-9]\+\(.*\)/pkgrel=$new_pkgrel\1/" PKGBUILD
+
+sed -i 's/-DCMAKE_BUILD_TYPE=Release/-DCMAKE_BUILD_TYPE=MinSizeRel/' PKGBUILD # size is the main reason we build our own clang
+sed -i 's/-DLLVM_TARGETS_TO_BUILD=".*"/-DLLVM_TARGETS_TO_BUILD="host"/' PKGBUILD # we don't need any cross-compilation targets
+sed -i 's/-DLLVM_ENABLE_SPHINX=ON/-DLLVM_ENABLE_SPHINX=OFF/' PKGBUILD # we don't need to spend time building documentation that we don't ship
+sed -n '/^check()/{p;:a;N;/\n}/!ba;s/.*\n/echo \n/};p' -i PKGBUILD # skip about an hour of linker tests
+
+
+cleanup