Install qjsc as part of the install target

[saghul]

Fixes: #730

[saghul]

Sample run:

Install the project...
-- Install configuration: "Release"
-- Installing: /tmp/local/include/quickjs.h
-- Installing: /tmp/local/bin/qjs
-- Installing: /tmp/local/bin/qjsc
-- Installing: /tmp/local/lib/libqjs.a
-- Installing: /tmp/local/lib/cmake/quickjs/qjsConfig.cmake
-- Installing: /tmp/local/lib/cmake/quickjs/qjsConfig-release.cmake
-- Installing: /tmp/local/share/doc/quickjs/LICENSE
-- Installing: /tmp/local/share/doc/quickjs/examples
-- Installing: /tmp/local/share/doc/quickjs/examples/test_point.js
-- Installing: /tmp/local/share/doc/quickjs/examples/hello.js
-- Installing: /tmp/local/share/doc/quickjs/examples/test_fib.js
-- Installing: /tmp/local/share/doc/quickjs/examples/fib_module.js
-- Installing: /tmp/local/share/doc/quickjs/examples/point.c
-- Installing: /tmp/local/share/doc/quickjs/examples/fib.c
-- Installing: /tmp/local/share/doc/quickjs/examples/pi_bigint.js
-- Installing: /tmp/local/share/doc/quickjs/examples/hello_module.js