The unary operator _Pragma allows a preprocessor macro to be
contained in a pragma directive. A _Pragma expression has
the following form:
>>-_Pragma--(--string_literal--)-------------------------------><
The string_literal may be prefixed with L, making it a wide-string literal.
The string literal is destringized and tokenized. The resulting sequence of tokens is processed as if it appeared in a pragma directive. For example:
_Pragma ( "align(power)" )
would be equivalent to
#pragma align(power)
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