package/mraa: fix toolchain requirements

package/mraa: fix toolchain requirements

New version of mraa has some extra toolchain requirements, added
dependency on !BR2_STATIC_LIBS and BR2_INSTALL_LIBSTDCPP

Fixes:
- http://autobuild.buildroot.net/results/f2829a0aff5bd6f73a837c813f20de5df33c7606
- http://autobuild.buildroot.net/results/b4434724ac810b35913a5e49b43e27e0418b5b9c
- http://autobuild.buildroot.net/results/6c7f19ea9757b483c3c7fe35d72ce9f9304f5919
- http://autobuild.buildroot.net/results/1c2bbeda09a695af2e53b0f72a116e6abef94b23
- http://autobuild.buildroot.net/results/7ea000298a4806040d9ec6140097eb3036440ee9

Signed-off-by: Pieterjan Camerlynck <pieterjan.camerlynck@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>