[libc][docs][NFC] Documentation consolidation and de-duplication (#187385)

Summary:
Integrated a series of quick documentation cleanups for LLVM-libc. This
update focuses on de-duplicating core conventions (naming and
namespaces) across multiple developer and contribution guides, and
addresses empty platform stubs for UEFI.

Changes:

* libc/docs/contributing.rst: Removed duplicated code style rules and
provided a link to dev/code_style.rst.
* libc/docs/dev/clang_tidy_checks.rst: Removed redundant namespace
explanations and linked to dev/code_style.rst.
* libc/docs/dev/implementation_standard.rst: Removed repetitive notes
about LIBC_NAMESPACE_DECL and linked to the authoritative reference.
* libc/docs/uefi/support.rst & libc/docs/uefi/using.rst: Added
early-stage bring-up warnings and pointed to the config directory for
the source of truth.

libc/docs/contributing.rst

@@ -18,18 +18,11 @@ a list of open projects that one can start with:
    ask if you can help take over.
 
 #. **Cleanup code-style** - The libc project follows the general
-   `LLVM style <https://llvm.org/docs/CodingStandards.html>`_ but differs in a
-   few aspects: We use ``snake_case`` for non-constant variable and function
-   names,``CamelCase`` for internal type names (those which are not defined in a
-   public header), and ``CAPITALIZED_SNAKE_CASE`` for constants. When we started
-   working on the project, we started using the general LLVM style for
-   everything. However, for a short period, we switched to the style that is
-   currently followed by the `LLD project <https://github.com/llvm/llvm-project/tree/main/lld>`_.
-   But, considering that we implement a lot of functions and types whose names
-   are prescribed by the standards, we have settled on the style described above.
-   However, we have not switched over to this style in all parts of the ``libc``
-   directory. So, a simple but mechanical project would be to move the parts
-   following the old styles to the new style.
+   `LLVM style <https://llvm.org/docs/CodingStandards.html>`_ with specific
+   conventions for naming (``snake_case`` for functions, ``CamelCase`` for
+   types). See the :ref:`code_style` page for the authoritative reference.
+   Mechanical projects to move parts following old styles to the current
+   conventions are welcome.
 
 #. **Implement Linux syscall wrappers** - A large portion of the POSIX API can
    be implemented as syscall wrappers on Linux. A good number have already been

libc/docs/dev/clang_tidy_checks.rst

@@ -43,10 +43,9 @@ implementation-in-namespace
 ---------------------------
 Check name: ``llvmlibc-implementation-in-namespace``.
 
-It is part of our implementation standards that all implementation pieces live
-under the ``LIBC_NAMESPACE_DECL`` namespace. This prevents pollution of the
-global namespace. Without a formal check to ensure this, an implementation
-might compile and pass unit tests, but not produce a usable libc function.
+All LLVM-libc implementation constructs must be enclosed in the
+``LIBC_NAMESPACE_DECL`` namespace. See :ref:`code_style` for the full technical
+rationale and macro definitions.
 
 This check ensures that top-level declarations in a translation unit are
 enclosed within the ``LIBC_NAMESPACE_DECL`` namespace.

libc/docs/dev/implementation_standard.rst

@@ -34,9 +34,9 @@ example. The ``isalpha`` function will be declared in an internal header file
 
     #endif LLVM_LIBC_SRC_CTYPE_ISALPHA_H
 
-Notice that the ``isalpha`` function declaration is nested inside the namespace
-``LIBC_NAMESPACE_DECL``. All implementation constructs in LLVM-libc are declared
-within the namespace ``LIBC_NAMESPACE_DECL``.
+All LLVM-libc implementation constructs must be enclosed in the
+``LIBC_NAMESPACE_DECL`` namespace. See :ref:`code_style` for the full technical
+rationale and macro definitions.
 
 ``.cpp`` File Structure
 -----------------------

libc/docs/uefi/support.rst

@@ -9,6 +9,12 @@ Supported Functions
 The follow functions and headers are supported at least partially in
 UEFI. Some functions are implemented fully for UEFI.
 
+.. note::
+   LLVM-libc support for UEFI is currently in the early bring-up phase. The
+   tables below are placeholders; for the current source of truth on
+   implemented functions, please refer to ``libc/config/uefi/entrypoints.txt``
+   in the source tree.
+
 ctype.h
 -------
 

libc/docs/uefi/using.rst

@@ -11,3 +11,8 @@ Once you have finished :ref:`building<libc_uefi_building>` the UEFI C library
 it can be used to run libc or libm functions inside of UEFI Images. Currently,
 not all C standard functions are supported in UEFI. Consult the :ref:`list of
 supported functions<libc_uefi_support>` for a comprehensive list.
+
+.. note::
+   LLVM-libc support for UEFI is currently in the early bring-up phase. For
+   the current source of truth on implemented functions, please refer to
+   ``libc/config/uefi/entrypoints.txt`` in the source tree.