Improve vala to support to generate libraries and bindings

[waruqi]

https://wiki.gnome.org/Projects/Vala/Bindings
https://wiki.gnome.org/Projects/Vala/SharedLibSample

[waruqi]

shared library

add_rules("mode.release", "mode.debug")

add_requires("glib")

target("mymath")
    set_kind("shared")
    add_rules("vala")
    add_files("src/mymath.vala")
    add_values("vala.header", "mymath.h")
    add_values("vala.vapi", "mymath-1.0.vapi")
    add_packages("glib")

target("test")
    set_kind("binary")
    add_deps("mymath")
    add_rules("vala")
    add_files("src/main.vala")
    add_packages("glib")

$ xmake -v
[ 12%]: compiling.vala src/mymath.vala
/usr/bin/valac -C -b build/.gens/mymath/linux/x86_64/release/src --vapi=build/linux/x86_64/release/mymath-1.0.vapi -H build/linux/x86_64/release/mymath.h src/mymath.vala
/usr/bin/ccache /usr/bin/gcc -c -m64 -fPIC -O3 -isystem build/linux/x86_64/release -isystem /usr/include/glib-2.0 -isystem /usr/lib/x86_64-linux-gnu/glib-2.0/include -DNDEBUG -o build/.objs/mymath/linux/x86_64/release/gens/src/mymath.c.o build/.gens/mymath/linux/x86_64/release/src/mymath.c
[ 25%]: linking.release libmymath.so
/usr/bin/g++ -o build/linux/x86_64/release/libmymath.so build/.objs/mymath/linux/x86_64/release/gens/src/mymath.c.o -shared -fPIC -m64 -L/usr/lib/x86_64-linux-gnu -s -lgobject-2.0 -lglib-2.0 -lpcre -lz -lffi -lffi_pic
checking for g++ ... /usr/bin/g++
checking for the linker (ld) ... g++
[ 62%]: compiling.vala src/main.vala
/usr/bin/valac -C -b build/.gens/test/linux/x86_64/release/src build/linux/x86_64/release/mymath-1.0.vapi src/main.vala
/usr/bin/ccache /usr/bin/gcc -c -m64 -fvisibility=hidden -O3 -isystem /usr/include/glib-2.0 -isystem /usr/lib/x86_64-linux-gnu/glib-2.0/include -isystem build/linux/x86_64/release -DNDEBUG -o build/.objs/test/linux/x86_64/release/gens/src/main.c.o build/.gens/test/linux/x86_64/release/src/main.c
checking for /usr/bin/g++ ... ok
checking for flags (-Wl,-rpath=@loader_path) ... ok
> g++ "-Wl,-rpath=@loader_path" "-m64" "-m64"
[ 75%]: linking.release test
/usr/bin/g++ -o build/linux/x86_64/release/test build/.objs/test/linux/x86_64/release/gens/src/main.c.o -m64 -L/usr/lib/x86_64-linux-gnu -Lbuild/linux/x86_64/release -Wl,-rpath=$ORIGIN -s -lgobject-2.0 -lglib-2.0 -lpcre -lz -lffi -lffi_pic -lmymath
[100%]: build ok!

static library

add_rules("mode.release", "mode.debug")

add_requires("glib")

target("mymath")
    set_kind("static")
    add_rules("vala")
    add_files("src/mymath.vala")
    add_values("vala.header", "mymath.h")
    add_values("vala.vapi", "mymath-1.0.vapi")
    add_packages("glib")

target("test")
    set_kind("binary")
    add_deps("mymath")
    add_rules("vala")
    add_files("src/main.vala")
    add_packages("glib")

[waruqi]

examples: https://github.com/xmake-io/xmake/blob/dev/tests/projects/vala/sharedlib/xmake.lua