Pull in r325478 from upstream clang trunk (by Ivan A. Kosarev):

Pull in r325478 from upstream clang trunk (by Ivan A. Kosarev):

  [CodeGen] Initialize large arrays by copying from a global

  Currently, clang compiles explicit initializers for array elements
  into series of store instructions. For large arrays of built-in types
  this results in bloated output code and significant amount of time
  spent on the instruction selection phase. This patch fixes the issue
  by initializing such arrays with global constants that store the
  binary image of the initializer.

  Differential Revision: https://reviews.llvm.org/D43181

This should fix a compiler hang (and excessive memory usage) while
building the science/rmg port.

Approved by:	re (kib)
Reported by:	yuri@tsoft.com
See also:	https://bugs.llvm.org/show_bug.cgi?id=38798
MFC after:	3 days