[libc-commits] [libc] [libc][docs] Update docs to reflect new headergen (PR #102381)

[Joseph Huber via libc-commits]

================
@@ -8,27 +8,97 @@ Full Host Build
    :depth: 1
    :local:
 
+.. note:: 
+   Fullbuild requires running headergen, which is a python program that depends on
+   pyyaml. The minimum versions are listed on the :ref:`header_generation`
+   page, as well as additional information.
+
 In this document, we will present a recipe to build the full libc for the host.
 When we say *build the libc for the host*, the goal is to build the libc for
-the same system on which the libc is being built. Also, we will take this
-opportunity to demonstrate how one can set up a *sysroot* (see the documentation
+the same system on which the libc is being built. First, we will explain how to
+build for developing LLVM-libc, then we will explain how to build LLVM-libc as
+part of a complete toolchain.
+
+Configure the build for development
+===================================
+
+
+Below is the list of commands for a simple recipe to build LLVM-libc for
+development. In this we've set the Ninja generator, set the build type to
+"Debug", and enabled the Scudo allocator. This build also enables generating the
+documentation and verbose cmake logging, which are useful development features.
+
+.. note::
+   if your build fails with an error saying the compiler can't find
+   ``<asm/unistd.h>`` or similar then you're probably missing the symlink from
+   ``/usr/include/asm`` to ``/usr/include/<HOST TRIPLE>/asm``. Installing the
+   ``gcc-multilib`` package creates this symlink, or you can do it manually with
+   this command:
+   ``sudo ln -s /usr/include/<HOST TRIPLE>/asm /usr/include/asm``
+   (your host triple will probably be similar to ``x86_64-linux-gnu``)
+
+.. code-block:: sh
+
+   $> cd llvm-project  # The llvm-project checkout
+   $> mkdir build
+   $> cd build
+   $> cmake ../runtimes \
----------------
jhuber6 wrote:

Hm, we might need to refine the  weird hacky logic for `set(NEED_LIBC_HDRGEN FALSE)`

https://github.com/llvm/llvm-project/pull/102381