The recent implementation of some asm function in libgcc added
__popcountqi2 and __parityqi2. This patch makes these functions
available as __builtin_avr_popcount8 resp. __builtin_avr_parity8.

Moreover, just out of a mood, I wrote a builtin for 1<<n.
1<<n is sometimes used to set a variable SFR bit. The builtin supplies
a fast, loop-free implementation.

The nice thing is that all these can represented explicitly so that
gcc sees what's going on and can fold if it sees operation on a
compile time constant.

Johann

	* config/avr/avr.c (avr_init_builtins, avr_builtin_id,
	bdesc_1arg): Add support for __builtin_avr_parity8,
	__builtin_avr_popcount8, __builtin_avr_pow2.
	(adjust_insn_length): Filter out "ashlqi2_1" insn in length
	computation.
	* config/avr/avr.c (avr_cpu_cpp_builtins): New builtin defines for
	__BUILTIN_AVR_PARITY8, __BUILTIN_AVR_POPCOUNT8,	__BUILTIN_AVR_POW2.
	* config/avr/avr.md (parityqi2): New expander.
	(popcountqi2): New expander.
	(*parityqihi2.libgcc): New insn.
	(*popcountqi2.libgcc): New insn.
	(ashlqi2_1): New insn.
	* doc/extend.texi (AVR Built-in Functions): Document new builtins
	__builtin_avr_parity8, __builtin_avr_popcount8,
	__builtin_avr_pow2.