Updates to Win64EH.h structures.

Change member types of RuntimeFunction and UnwindInfo from uint64_t to
uint32_t:
These members represent addresses. According to MSDN, they are image
relative, that is, they are 32-bit offsets from the starting address
of the image that contains the function table entry.
See MSDN for more information:
RUNTIME_FUNCTION: http://msdn.microsoft.com/en-us/library/ft9x1kdx.aspx
UNWIND_INFO: http://msdn.microsoft.com/en-us/library/ddssxxy8.aspx

Make Win64.h platform-neutral:
The standard types unit8_t, uint16_t and uint32_t are replaced with
their counterparts from Endian.h. Accessor functions are introduced to
replace bit fields.

Patch by João Matos and Kai Nacke.

llvm-svn: 169414