Emit the DW_AT_type for a C++ static member definition

if it is more specific than the one in its DW_AT_specification.

If a static member is an array, the translation unit containing the
member definition may have a more specific type (including its length)
than TUs only seeing the class declaration. This patch adds a
DW_AT_type to the member's DW_TAG_variable in addition to the
DW_AT_specification in these cases. The member type in the
DW_AT_specification still shows the more generic type (without the
length) to avoid defeating type uniquing.

The DWARF standard discourages “duplicating” a DW_AT_type in a member
variable definition but doesn’t explicitly forbid it.  Having the more
specific type (with the array length) available is what allows the
debugger to print the contents of a static array member variable.

https://reviews.llvm.org/D26368
rdar://problem/28706946

llvm-svn: 286302