[OpenMP] Add type to firstprivate symbol for const firstprivate values

Clang will create a global value put in constant memory if an aggregate value
is declared firstprivate in the target device. The symbol name only uses the
name of the firstprivate variable, so symbol name conflicts will occur if the
variable is allowed to have different types through templates. An example of
this behvaiour is shown in https://godbolt.org/z/EsMjYh47n. This patch adds the
mangled type name to the symbol to avoid such naming conflicts. This fixes
https://bugs.llvm.org/show_bug.cgi?id=50642.

Reviewed By: ABataev

Differential Revision: https://reviews.llvm.org/D103995