add note about headergen needing pyyaml to fullbuild docs

Author: michaelrj-google

libc/docs/dev/header_generation.rst

@@ -1,3 +1,5 @@
+.. _header_generation:
+
 Generating Public and Internal headers
 ======================================
 

libc/docs/full_cross_build.rst

@@ -8,6 +8,11 @@ Full Cross 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 recipes to cross build the full libc. When we
 say *cross build* a full libc, we mean that we will build the full libc for a
 target system which is not the same as the system on which the libc is being

libc/docs/full_host_build.rst

@@ -8,6 +8,11 @@ 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. First, we will explain how to

libc/docs/fullbuild_mode.rst

@@ -4,6 +4,11 @@
 Fullbuild Mode
 ==============
 
+.. 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.
+
 The *fullbuild* mode of LLVM's libc is the mode in which it is to be used as
 the only libc (as opposed to the :ref:`overlay_mode` in which it is used along
 with the system libc.) In order to use it as the only libc, one will have to