This avoids the need to dynamically relocate each pointer in the table.
To make this work, this PR also moves the binary search of intrinsic
names to an internal function with an adjusted signature, and switches
the unittesting to test against actual intrinsics.
This reverts commit c2b61fcb3cd4ffa286b24437b7b6d66f0dee6c25.
Intrinsic namespace contains memcpy which is a naming conflict with
memcpy from string.h header.
Rename the function to reflect its correct behavior and to be consistent
with `Module::getOrInsertFunction`. This is also in preparation of
adding a new `Intrinsic::getDeclaration` that will have behavior similar
to `Module::getFunction` (i.e, just lookup, no creation).
