boost: enable for clangarm64

Disable boost context as there is no Windows arm64 implementation
(#9045).  Also disable coroutine and fiber as they depend on context.

mingw-w64-boost/PKGBUILD

@@ -8,10 +8,10 @@ pkgbase=mingw-w64-${_realname}
 pkgname="${MINGW_PACKAGE_PREFIX}-${_realname}"
 pkgver=1.78.0
 _boostver=${pkgver//./_}
-pkgrel=2
+pkgrel=3
 pkgdesc="Free peer-reviewed portable C++ source libraries (mingw-w64)"
 arch=('any')
-mingw_arch=('mingw32' 'mingw64' 'ucrt64' 'clang64' 'clang32')
+mingw_arch=('mingw32' 'mingw64' 'ucrt64' 'clang64' 'clang32' 'clangarm64')
 url="https://www.boost.org/"
 license=('custom')
 depends=("${MINGW_PACKAGE_PREFIX}-gcc-libs"
@@ -150,6 +150,11 @@ setb2args() {
     -sZLIB_LIBPATH=${MINGW_PREFIX}/lib \
     -d2 \
     -q"
+    if [[ "${CARCH}" == "aarch64" ]]; then
+      # boost context does not yet have an implementation for Windows ARM64
+      # coroutine and fiber depend on context
+      b2args+=" --without-context --without-coroutine --without-fiber"
+    fi
 }
 
 build() {