This is step 4 of
https://discourse.llvm.org/t/rfc-customizable-namespace-to-allow-testing-the-libc-when-the-system-libc-is-also-llvms-libc/73079

Update the rounding logic for generic hypot function so that it will round correctly with all rounding modes.

Reviewed By: sivachandra, zimmermann6

Differential Revision: https://reviews.llvm.org/D117590

Apply the formatting rules that were applied to the libc/src directory
to the libc/test directory, as well as the files in libc/utils that are
included by the tests. This does not include automated enforcement.

Reviewed By: sivachandra, lntue

Differential Revision: https://reviews.llvm.org/D116127

I missed the MPFR tests in my previous commit. They have now been fixed
to not fail the prefix check in the test macro.

Summary:
Having a consistent prefix makes selecting all of the llvm libc tests
easier on any platform that is also using the gtest framework.
This also modifies the TEST and TEST_F macros to enforce this change
moving forward.

Reviewers: sivachandra

Subscribers:

Refactor src/math/hypotf.cpp and test/src/math/hypotf_test.cpp and reuse them for hypot and hypot_test

Differential Revision: https://reviews.llvm.org/D91831

This switches all of the files in src/string, src/math, and
test/src/math from using relative paths (e.g. `#include “include/string.h”`)
to global paths (e.g. `#include <string.h>`) to make bringing up those
functions on other platforms, such as fuchsia, easier.

Reviewed By: sivachandra

Differential Revision: https://reviews.llvm.org/D91394

Truncating the sum of squares, and then use shift-and-add algorithm to compute its square root.
Required MPFR testing infra is updated in https://reviews.llvm.org/D87514

Differential Revision: https://reviews.llvm.org/D87516