Add blurb for PowerPC.

- Delay slot filler pass can now search successor blocks for instructions to

  fill delay slots (use option -disable-mips-df-succbb-search=false).

PowerPC Target

--------------

New features and improvements:

- PowerPC now supports an assembly parser.

- Support added for thread-local storage.  64-bit ELF subtarget only.

- Support added for medium and large code model (-mcmodel=medium,large).

  Medium code model is now the default.  64-bit ELF subtarget only.

- Improved register allocation (fewer reserved registers).

- 64-bit atomic load and store are now supported.

- Improved code generation for unaligned memory accesses of scalar types.

- Improved performance of floating-point divide and square root

  with -ffast-math.

- Support for predicated returns.

- Improved code generation for comparisons.

- Support added for inline setjmp and longjmp.

- Support added for many instructions introduced in PowerISA 2.04, 2.05,

  and 2.06.

- Improved spill code for vector registers.

- Support added for -mno-altivec.

- ABI compatibility fixes for complex parameters, 128-bit integer parameters,

  and varargs functions.  64-bit ELF subtarget only.

Loop Vectorizer

---------------