build: add PKGBUILD for libx11 with msan support

tools/pacman/libx11_msan/PKGBUILD

@@ -0,0 +1,42 @@
+# Modified version of the official `pacman` PKGBUILD for libx11 with msan support
+# original: https://gitlab.archlinux.org/archlinux/packaging/packages/libx11/-/blob/main/PKGBUILD?ref_type=heads"
+
+pkgname=libx11
+pkgver=1.8.12
+pkgrel=1
+pkgdesc="X11 client-side library"
+arch=(x86_64)
+url="https://gitlab.freedesktop.org/xorg/lib/libx11"
+depends=('libxcb' 'glibc' 'xorgproto')
+makedepends=('xorg-util-macros' 'xtrans' 'clang')
+license=('MIT AND X11')
+source=(https://xorg.freedesktop.org//releases/individual/lib/libX11-${pkgver}.tar.xz{,.sig})
+sha512sums=('cb7a284d9081a8b67f7d8568d56dc403a4b787e46ac497b07768d236084c01f80f4ea2ebd814f950ac9738adc3baea3912932fc333858195c4f8217744b6f730'
+            'SKIP')
+
+build() {
+  cd libX11-${pkgver}
+
+  ### msan ###
+  clang --version
+  export CC="$(which clang) -fno-omit-frame-pointer -g -fsanitize=memory -fsanitize-memory-track-origins"
+
+  ./configure --prefix=/usr \
+    --disable-static \
+    --disable-xf86bigfont
+  sed -i -e 's/ -shared / -Wl,-O1,--as-needed\0/g' libtool
+  make
+}
+
+check() {
+  cd libX11-${pkgver}
+  make check
+}
+
+package() {
+  cd "libX11-${pkgver}"
+  make DESTDIR="${pkgdir}" install
+
+  install -d -m755 "${pkgdir}/usr/share/licenses/${pkgname}"
+  install -m644 COPYING "${pkgdir}/usr/share/licenses/${pkgname}/"
+}