Reviewed By: michaelrj

Differential Revision: https://reviews.llvm.org/D112673

The idea is to move all pieces related to the actual libc sources to the
"src" directory. This allows downstream users to ship and build just the
"src" directory.

Reviewed By: michaelrj

Differential Revision: https://reviews.llvm.org/D112653

Also, this adds unit tests to check that limits.h complies with the C
standard.

Reviewed By: sivachandra

Differential Revision: https://reviews.llvm.org/D110643

This clean-up removes checks for _WIN64, as the _WIN32 macro returns 1
whenever the compilation targe is 32- or 64-bit ARM.

Reviewed By: aeubanks

Differential Revision: https://reviews.llvm.org/D106706

This addition reads command line input to run specific single tests
within a larger call to run all the tests for a particular function.
When the user adds a second argument to the command line, the code skips
all the tests that don't match the user's specified binary. If the user
doesn't specify a test correctly and/or no tests are run, a failure
message prints.

Reviewed By: sivachandra, aeubanks

Differential Revision: https://reviews.llvm.org/D105843

Changed where an #endif was placed because previously it
prevented three macro definitions from being enable in Windows.

Reviewed By: sivachandra

Differential Revision: https://reviews.llvm.org/D106087

This is useful when bringing up LLVM libc on a new OS on which we do not
yet have the subprocess related helper functions.

These libraries do not depend on LLVM libraries anymore so they do not
have to be added using add_llvm_library.

This patch provides `TYPED_TEST` and `TYPED_TEST_F` (similar in functionnality to gtest).
This is needed to extensively test building blocks for memory functions.

Example for `TYPED_TEST_F`:
```
template <typename T> class LlvmLibcMyTestFixture : public testing::Test {};

using Types = testing::TypeList<char, int, long>;

TYPED_TEST_F(LlvmLibcMyTestFixture, Simple, Types) {
  EXPECT_LE(sizeof(ParamType), 8UL);
}
```

Example for `TYPED_TEST`:
```
using Types = testing::TypeList<char, int, long>;

TYPED_TEST(LlvmLibcMyTest, Simple, Types) {
  EXPECT_LE(sizeof(ParamType), 8UL);
}
```

`ParamType` is displayed as fully qualified canonical type which can be difficult to read, the user can provide a more readable name by using the `REGISTER_TYPE_NAME` macro.

Differential Revision: https://reviews.llvm.org/D100631