[committed] Fix mips-linux-gnu mips.exp failures

[Uros Bizjak]

Hello!

> This patch therefore adds a new mips16_attribute target selector.
> It also adds a new dg-add-options feature that tries to add options
> that enable MIPS16 code generation (-mno-abicalls -fno-pic).  Thus
> normal mips-linux-gnu tests do run the compile-only MIPS16 tests
> but, for example, --target_board unix/-fpic doesn't.
>
>
> gcc/testsuite/
> 	* lib/target-supports.exp (add_options_for_mips16_attribute)
> 	(check_effective_target_mips16_attribute): New functions.

Should we move mips specific procedures (i.e. 
check_effective_target_mpaired_single, check_effective_target_mips64 and 
new add_options_for_mips16_attribute and 
check_effective_target_mips16_attribute) from lib/target-supports.exp to 
gcc.target/mips/mips.exp? i386 has its private check_effective_target_* 
procedures defined in gcc.target/i386/i386.exp and it works just fine.

Thanks,
Uros.