Add package for my build environment

* Set consistent Android API level
* Ensure make utilizes all CPU cores if `MAKEFLAGS` are otherwise cleared
  via `!buildflags` because this is nevertheless wanted in mingw-w64 and
  android packages (that usually set `!buildflags`)
* Ensure required devel packages are installed

buildenv/default/PKGBUILD

@@ -0,0 +1,18 @@
+pkgname=buildenv
+pkgver=1
+pkgrel=2
+pkgdesc='Build environment for my Arch Linux package builds'
+arch=('any')
+license=('GPL-2.0-or-later')
+url='https://github.com/Martchus/PKGBUILDs'
+depends=('base-devel' 'multilib-devel')
+source=(android.sh parallel.sh)
+sha256sums=(SKIP SKIP)
+
+package() {
+  cd "$srcdir"
+  mkdir -p "$pkgdir/usr/share/makepkg/buildenv"
+  for src in android parallel; do
+    cp -v "$src.sh" "$pkgdir/usr/share/makepkg/buildenv/$src.sh"
+  done
+}

buildenv/default/android.sh

@@ -0,0 +1,12 @@
+#!/usr/bin/bash
+
+[[ -n "$LIBMAKEPKG_BUILDENV_ANDROID_SH" ]] && return
+LIBMAKEPKG_BUILDENV_ANDROID_SH=1
+
+buildenv_functions+=('buildenv_android')
+buildenv_vars+=('ANDROID_MINIMUM_PLATFORM')
+
+buildenv_android() {
+	# set minimum Android version to Android 7.0
+	ANDROID_MINIMUM_PLATFORM=24
+}

buildenv/default/parallel.sh

@@ -0,0 +1,10 @@
+#!/usr/bin/bash
+
+[[ -n "$LIBMAKEPKG_BUILDENV_PARALLEL_SH" ]] && return
+LIBMAKEPKG_BUILDENV_PARALLEL_SH=1
+
+buildenv_functions+=('buildenv_parallel')
+
+buildenv_parallel() {
+	[[ $MAKEFLAGS ]] || MAKEFLAGS=-j$(nproc)
+}