[vendor] Ensure that all cflags are properly quoted.
[vendor] Ensure that all cflags are properly quoted.

Before it looked like the `-isysroot \"#{sdk_path}\"` part of the cflags
would terminate the string passed to the `--cflags` option.

Now all the contents of the `--cflags` option is quoted using
single-quotes instead.

katsuyoshi/RubyMotion,HipByte/RubyMotion,incbee/RubyMotion,jjaffeux/RubyMotion,beni55/RubyMotion,katsuyoshi/RubyMotion,jjaffeux/RubyMotion,HipByte/RubyMotion,jjaffeux/RubyMotion,beni55/RubyMotion,beni55/RubyMotion,hboon/RubyMotion,hboon/RubyMotion,incbee/RubyMotion,incbee/RubyMotion,katsuyoshi/RubyMotion,beni55/RubyMotion,incbee/RubyMotion,jjaffeux/RubyMotion,HipByte/RubyMotion,katsuyoshi/RubyMotion,hboon/RubyMotion