Add storage to Symbol for analysis result bool forced_llvm_bool().

[AlexMWells]

Results of a compare_op and other ops with logically boolean
results under certain conditions could be forced to be represented
in llvm as a boolean vs. an integer . This simplifies
code generation, and under batched execution is a requirement
to make efficient use of hardware masking registers by allowing a
vector of bools <16 x i1> vs. integers <16 x i32>. However the
underlying OIIO::TypeDesc as well as OSL does not support bools,
therefore they need to be promoted to integers when interacting with
other integer op's.
The value of forced_llvm_bool() is currently only respected during
batched execution. Forced bools should not be coalesced with regular
ints, only other forced bools.

Description

Tests

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