PR19767: DebugInfo emission of pointer constants.

In refactoring DwarfUnit::isUnsignedDIType I restricted it to only work
on values with signedness (unsigned or signed), asserting on anything
else (which did uncover some bugs). But it turns out that we do need to
emit constants of signless data, such as pointer constants - only null
pointer constants are known to need this so far, but it's conceivable
that there might be non-null pointer constants at some point (hardcoded
address offsets for device drivers?).

This patch just uses 'unsigned' for signless data such as pointer
constants. Arguably we could use signless representations
(DW_FORM_dataN) instead, allowing a trinary result from isUnsignedDIType
(signed, unsigned, signless), but this seems reasonable for now.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@209223 91177308-0d34-0410-b5e6-96231b3b80d8
Rewrite calculateDbgValueHistory to make it (hopefully) more transparent.

This change preserves the original algorithm of generating history
for user variables, but makes it more clear.

High-level description of algorithm:
Scan all the machine basic blocks and machine instructions in the order
they are emitted to the object file. Do the following:
1) If we see a DBG_VALUE instruction, add it to the history of the
corresponding user variable. Keep track of all user variables, whose
locations are described by a register.
2) If we see a regular instruction, look at all the registers it clobbers,
and terminate the location range for all variables described by these registers.
3) At the end of the basic block, terminate location ranges for all
user variables described by some register.

Although this change shouldn't be user-visible (the contents of .debug_loc section
should be the same), it changes some internal assumptions about the set
of instructions used to track the variable locations. Watching the bots.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@209225 91177308-0d34-0410-b5e6-96231b3b80d8
Fix test breakage introduced in r209223.

Oops, broke the broken enum constants again.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@209226 91177308-0d34-0410-b5e6-96231b3b80d8