Place static initializers on linux into the ".text.startup" section, so the...

Place static initializers on linux into the ".text.startup" section, so the linker can group them together for performance.

This only has an effect with fairly new binutils (2.21.51 or later). Other ELF targets probably want this as well, but on BSDs binutils is usually old so it doesn't matter.

llvm-svn: 142076