[lldb] Fix type conversion in the Scalar getters
The Scalar class claims to follow the C type conversion rules. This is
true for the Promote function, but it is not true for the implicit
conversions done in the getter methods.
These functions had a subtle bug: when extending the type, they used the
signedness of the *target* type in order to determine whether to do
sign-extension or zero-extension. This is not how things work in C,
which uses the signedness of the *source* type. I.e., C does
(sign-)extension before it does signed->unsigned conversion, and not the
other way around.
This means that: (unsigned long)(int)-1
is equal to (unsigned long)0xffffffffffffffff and not (unsigned long)0x00000000ffffffff
Unsurprisingly, we have accumulated code which depended on this
inconsistent behavior. It mainly manifested itself as code calling
"ULongLong/SLongLong" as a way to get the value of the Scalar object in
a primitive type that is "large enough". Previously, the ULongLong
conversion did not do sign-extension, but now it does.
This patch makes the Scalar getters consistent with the declared
semantics, and fixes the couple of call sites that were using it
Reviewers: teemperor, JDevlieghere
Differential Revision: https://reviews.llvm.org/D82772