[llvm-rc] Add integer expressions parsing ability. [7/8]
This allows the ints to be written as integer expressions evaluating to
unsigned 16-bit/32-bit integers.
All the expressions may use the following operators: + - & | ~, and
parentheses. Minus token - can be also unary. There is no precedence of
the operators other than the unary operators binding stronger than their
Differential Revision: https://reviews.llvm.org/D37022