Implement INDEX in the runtime, reusing some infrastructure
(with generalization and renaming as needed) put into place
for its cousins SCAN and VERIFY.
I did not implement full Boyer-Moore substring searching
for the forward case, but did accelerate some advancement on
mismatches.
I (re)implemented unit testing for INDEX in the new gtest
framework, combining it with the tests that have recently
been ported to gtest for SCAN and VERIFY.
Differential Revision: https://reviews.llvm.org/D98553
Move character tests to gtest, according to reviews from revision
D97349. Create a new temporary directory parallel to old runtime
unittests directory to facilitate the transition. Once patches for all
tests have been accepted using GTest, the old directory may be removed.
The new directory is required because LLVM's CMake unit test
infrastructure requires that the test depends on all source files in
the `CMAKE_CURRENT_SOURCE_DIR` directory.
Reviewed By: awarzynski
Differential Revision: https://reviews.llvm.org/D97403
peter klausler