Add support for a LLVM-based MinGW toolchain

Based on https://github.com/mstorsjo/llvm-mingw.

An advantage of a LLVM/Clang/LLD based mingw-w64 toolchain is that it has proper C++ threads which uses the win32 native thread functions directly. This toolchain might also be useful if we need to target Windows on ARM.

8.8/build.sh

@@ -41,31 +41,41 @@ if [ ! "$curr_revision" = "$revision" ]; then
 fi
 
 if [ "$initialize" = true ] ; then
-  # Copy settings
-  cp -f $work_dir/settings.mk $mxe_dir
-
   # Copy our customized tool
   cp -f $work_dir/tools/make-shared-from-static $mxe_dir/tools
-
-  # Copy our customized Meson cross file
-  cp -f $work_dir/mxe-crossfile.meson.in $mxe_dir/plugins/meson-wrapper/conf
 fi
 
-# Prepare MinGW directories
-mkdir -p $mxe_prefix/$target.$deps/mingw/{bin,include,lib}
+# The 'plugins' variable controls which plugins are in use.
+if [ "$LLVM" = "true" ]; then
+  echo "llvm-mingw plugin enabled"
+  plugins="$work_dir/plugins/llvm-mingw"
 
-# Build pe-util, handy for copying DLL dependencies.
-make pe-util MXE_TARGETS=`$mxe_dir/ext/config.guess`
+  # Copy LLVM settings
+  cp -f $work_dir/settings/llvm.mk $mxe_dir/settings.mk
+  cp -f $work_dir/settings/meson-llvm.in $mxe_dir/plugins/meson-wrapper/conf/mxe-crossfile.meson.in
+else
+  # Build with GCC 9.2
+  plugins="plugins/gcc9"
 
-# This variable controls which plugins are in use.
-# Build with GCC 9.2 and use the meson-wrapper.
-plugins="plugins/gcc9 plugins/meson-wrapper $work_dir"
+  # Copy GCC settings
+  cp -f $work_dir/settings/gcc.mk $mxe_dir/settings.mk
+  cp -f $work_dir/settings/meson-gcc.in $mxe_dir/plugins/meson-wrapper/conf/mxe-crossfile.meson.in
+fi
+
+# Use the meson-wrapper and our custom overrides
+plugins+=" plugins/meson-wrapper $work_dir"
 
 if [ "$MOZJPEG" = "true" ]; then
   echo "MozJPEG plugin enabled"
   plugins+=" $work_dir/plugins/mozjpeg"
 fi
 
+# Prepare MinGW directories
+mkdir -p $mxe_prefix/$target.$deps/mingw/{bin,include,lib}
+
+# Build pe-util, handy for copying DLL dependencies.
+make pe-util MXE_TARGETS=`$mxe_dir/ext/config.guess`
+
 # Build MXE's meson-wrapper (needed by pango, GDK-PixBuf, GLib and Orc), 
 # gendef (a tool for generating def files from DLLs)
 # and libvips (+ dependencies).

8.8/libheif.mk

@@ -9,8 +9,8 @@ $(PKG)_GH_CONF  := strukturag/libheif/releases,v
 $(PKG)_DEPS     := cc libde265 x265
 
 define $(PKG)_BUILD
-    cd '$(BUILD_DIR)' && $(TARGET)-cmake '$(SOURCE_DIR)' \
-        -DCMAKE_CXX_FLAGS='-Wno-error=unused-variable'
+    cd '$(BUILD_DIR)' && $(TARGET)-cmake '$(SOURCE_DIR)'
+
     $(MAKE) -C '$(BUILD_DIR)' -j '$(JOBS)'
     $(MAKE) -C '$(BUILD_DIR)' -j 1 install
 endef

8.8/mingw-std-threads.mk

@@ -2,12 +2,16 @@ PKG             := mingw-std-threads
 $(PKG)_WEBSITE  := https://github.com/meganz/mingw-std-threads
 $(PKG)_DESCR    := Standard threads implementation currently still missing on MinGW GCC on Windows
 $(PKG)_IGNORE   :=
-$(PKG)_VERSION  := 4e22f33
-$(PKG)_CHECKSUM := 92c051b9e5017ecbe85e0004677315f5a2784bca9f61db17655321788fe2594a
+# https://github.com/gitapi/repos/meganz/mingw-std-threads/tarball/bee085c0a6cb32c59f0b55c7bba976fe6dcfca7f
+$(PKG)_VERSION  := bee085c
+$(PKG)_CHECKSUM := eaa451e3db0b64b285ae2bc163e30f384ee933bb2765ed428b95686a94814dd7
 $(PKG)_GH_CONF  := meganz/mingw-std-threads/branches/master
-$(PKG)_DEPS     := cc
+$(PKG)_TYPE     := script
+$(PKG)_DEPS     :=
+
 
 define $(PKG)_BUILD
-    $(INSTALL) -d '$(PREFIX)/$(TARGET)/include/$(PKG)'
-    $(INSTALL) -m644 '$(SOURCE_DIR)/'*.h '$(PREFIX)/$(TARGET)/include/$(PKG)'
+    $(if $(findstring win32,$(TARGET)),\
+        $(INSTALL) -d '$(PREFIX)/$(TARGET)/include/$(PKG)'; \
+        $(INSTALL) -m644 '$(SOURCE_DIR)/'*.h '$(PREFIX)/$(TARGET)/include/$(PKG)')
 endef

8.8/orc.mk

@@ -18,6 +18,8 @@ endef
 
 define $(PKG)_BUILD
     '$(TARGET)-meson' \
+        --buildtype=release \
+        --strip \
         --libdir='lib' \
         --includedir='include' \
         -Dbenchmarks=disabled \