[libc][docs] stub out assert, errno, and locale (#118852)

[libc][docs] stub out assert, errno, and locale

These were the remaining c89 library headers (besides string.h and
stdlib.h; I
will split strings.rst in a follow up commit).

The macro support detection in docgen doesn't quite work for some of
these
headers. Add the stubs for these headers for now, and fix up docgen
later.

See the "NIST publication":
Link: https://www.open-std.org/jtc1/sc22/wg14/www/projects.html

libc/docs/headers/assert.rst

@@ -0,0 +1,27 @@
+.. include:: ../check.rst
+
+========
+assert.h
+========
+
+Macros
+======
+
+.. list-table::
+  :widths: auto
+  :align: center
+  :header-rows: 1
+
+  * - Macro
+    - Implemented
+    - C23 Standard Section
+    - POSIX.1-2024 Standard Section
+  * - __STDC_VERSION_ASSERT_H__
+    - |check|
+    - 7.2.1
+    -
+  * - assert
+    -
+    - 7.2.1
+    -
+

libc/docs/headers/errno.rst

@@ -0,0 +1,35 @@
+.. include:: ../check.rst
+
+=======
+errno.h
+=======
+
+Macros
+======
+
+.. list-table::
+  :widths: auto
+  :align: center
+  :header-rows: 1
+
+  * - Macro
+    - Implemented
+    - C23 Standard Section
+    - POSIX.1-2024 Standard Section
+  * - EDOM
+    -
+    - 7.5
+    -
+  * - EILSEQ
+    -
+    - 7.5
+    -
+  * - ERANGE
+    -
+    - 7.5
+    -
+  * - errno
+    -
+    - 7.5
+    -
+

libc/docs/headers/index.rst

@@ -4,9 +4,12 @@ Implementation Status
 .. toctree::
    :maxdepth: 1
 
+   assert
    complex
    ctype
+   errno
    fenv
+   locale
    math/index.rst
    search
    setjmp

libc/docs/headers/locale.rst

@@ -0,0 +1,63 @@
+.. include:: ../check.rst
+
+========
+locale.h
+========
+
+Macros
+======
+
+.. list-table::
+  :widths: auto
+  :align: center
+  :header-rows: 1
+
+  * - Macro
+    - Implemented
+    - C23 Standard Section
+    - POSIX.1-2024 Standard Section
+  * - LC_ALL
+    - |check|
+    - 7.11
+    -
+  * - LC_COLLATE
+    - |check|
+    - 7.11
+    -
+  * - LC_CTYPE
+    - |check|
+    - 7.11
+    -
+  * - LC_MONETARY
+    - |check|
+    - 7.11
+    -
+  * - LC_NUMERIC
+    - |check|
+    - 7.11
+    -
+  * - LC_TIME
+    - |check|
+    - 7.11
+    -
+
+Functions
+=========
+
+.. list-table::
+  :widths: auto
+  :align: center
+  :header-rows: 1
+
+  * - Function
+    - Implemented
+    - C23 Standard Section
+    - POSIX.1-2024 Standard Section
+  * - localeconv
+    - |check|
+    - 7.11.2.1
+    -
+  * - setlocale
+    - |check|
+    - 7.11.1.1
+    -

libc/utils/docgen/assert.json

@@ -0,0 +1,10 @@
+{
+  "macros": {
+    "__STDC_VERSION_ASSERT_H__": {
+      "c-definition": "7.2.1"
+    },
+    "assert": {
+      "c-definition": "7.2.1"
+    }
+  }
+}

libc/utils/docgen/errno.json

@@ -0,0 +1,16 @@
+{
+  "macros": {
+    "EDOM": {
+      "c-definition": "7.5"
+    },
+    "EILSEQ": {
+      "c-definition": "7.5"
+    },
+    "ERANGE": {
+      "c-definition": "7.5"
+    },
+    "errno": {
+      "c-definition": "7.5"
+    }
+  }
+}

libc/utils/docgen/locale.json

@@ -0,0 +1,30 @@
+{
+  "macros": {
+    "LC_ALL": {
+      "c-definition": "7.11"
+    },
+    "LC_COLLATE": {
+      "c-definition": "7.11"
+    },
+    "LC_CTYPE": {
+      "c-definition": "7.11"
+    },
+    "LC_MONETARY": {
+      "c-definition": "7.11"
+    },
+    "LC_NUMERIC": {
+      "c-definition": "7.11"
+    },
+    "LC_TIME": {
+      "c-definition": "7.11"
+    }
+  },
+  "functions": {
+    "setlocale": {
+      "c-definition": "7.11.1.1"
+    },
+    "localeconv": {
+      "c-definition": "7.11.2.1"
+    }
+  }
+}