[libc][docs] adds threads.h impl status docs (#89275)

Closes #88067.

Adding @nickdesaulniers for review.

Author: Flandini

libc/docs/index.rst

@@ -71,6 +71,7 @@ stages there is no ABI stability in any form.
    c23
    ctype
    signal
+   threads
 
 .. toctree::
    :hidden:

libc/docs/threads.rst

@@ -0,0 +1,88 @@
+.. include:: check.rst
+
+threads.h Functions
+===================
+
+.. list-table::
+  :widths: auto
+  :align: center
+  :header-rows: 1
+
+  * - Function
+    - Implemented
+    - Standard
+  * - call_once
+    - |check|
+    - 7.28.2.1
+  * - cnd_broadcast
+    - |check|
+    - 7.28.3.1
+  * - cnd_destroy
+    - |check|
+    - 7.28.3.2
+  * - cnd_init
+    - |check|
+    - 7.28.3.3
+  * - cnd_signal
+    - |check|
+    - 7.28.3.4
+  * - cnd_timedwait
+    -
+    - 7.28.3.5
+  * - cnd_wait
+    - |check|
+    - 7.28.3.6
+  * - mtx_destroy
+    - |check|
+    - 7.28.4.1
+  * - mtx_init
+    - |check|
+    - 7.28.4.2
+  * - mtx_lock
+    - |check|
+    - 7.28.4.3
+  * - mtx_timedlock
+    -
+    - 7.28.4.4
+  * - mtx_trylock
+    -
+    - 7.28.4.5
+  * - mtx_unlock
+    - |check|
+    - 7.28.4.6
+  * - thrd_create
+    - |check|
+    - 7.28.5.1
+  * - thrd_current
+    - |check|
+    - 7.28.5.2
+  * - thrd_detach
+    - |check|
+    - 7.28.5.3
+  * - thrd_equal
+    - |check|
+    - 7.28.5.4
+  * - thrd_exit
+    - |check|
+    - 7.28.5.5
+  * - thrd_join
+    - |check|
+    - 7.28.5.6
+  * - thrd_sleep
+    -
+    - 7.28.5.7
+  * - thrd_yield
+    -
+    - 7.28.5.8
+  * - tss_create
+    - |check|
+    - 7.28.6.1
+  * - tss_delete
+    - |check|
+    - 7.28.6.2
+  * - tss_get
+    - |check|
+    - 7.28.6.3
+  * - tss_set
+    - |check|
+    - 7.28.6.4

libc/utils/docgen/threads.json

@@ -0,0 +1,87 @@
+{
+  "macros": {
+    "ONCE_FLAG_INIT": {
+      "defined": "7.28.1.3"
+    },
+    "TSS_DTOR_ITERATIONS": {
+      "defined": "7.28.1.3"
+    }
+  },
+  "functions": {
+    "call_once": {
+      "defined": "7.28.2.1"
+    },
+    "cnd_broadcast": {
+      "defined": "7.28.3.1"
+    },
+    "cnd_destroy": {
+      "defined": "7.28.3.2"
+    },
+    "cnd_init": {
+      "defined": "7.28.3.3"
+    },
+    "cnd_signal": {
+      "defined": "7.28.3.4"
+    },
+    "cnd_timedwait": {
+      "defined": "7.28.3.5"
+    },
+    "cnd_wait": {
+      "defined": "7.28.3.6"
+    },
+    "mtx_destroy": {
+      "defined": "7.28.4.1"
+    },
+    "mtx_init": {
+      "defined": "7.28.4.2"
+    },
+    "mtx_lock": {
+      "defined": "7.28.4.3"
+    },
+    "mtx_timedlock": {
+      "defined": "7.28.4.4"
+    },
+    "mtx_trylock": {
+      "defined": "7.28.4.5"
+    },
+    "mtx_unlock": {
+      "defined": "7.28.4.6"
+    },
+    "thrd_create": {
+      "defined": "7.28.5.1"
+    },
+    "thrd_current": {
+      "defined": "7.28.5.2"
+    },
+    "thrd_detach": {
+      "defined": "7.28.5.3"
+    },
+    "thrd_equal": {
+      "defined": "7.28.5.4"
+    },
+    "thrd_exit": {
+      "defined": "7.28.5.5"
+    },
+    "thrd_join": {
+      "defined": "7.28.5.6"
+    },
+    "thrd_sleep": {
+      "defined": "7.28.5.7"
+    },
+    "thrd_yield": {
+      "defined": "7.28.5.8"
+    },
+    "tss_create": {
+      "defined": "7.28.6.1"
+    },
+    "tss_delete": {
+      "defined": "7.28.6.2"
+    },
+    "tss_get": {
+      "defined": "7.28.6.3"
+    },
+    "tss_set": {
+      "defined": "7.28.6.4"
+    }
+  }
+}