a few type fixes (#172)

Author: mochaaP

src/libtypenamespace/addedData.csv

@@ -119,3 +119,4 @@ sourceset_module::source_set,0.51.0
 wayland_module::find_protocol,0.62.0
 wayland_module::scan_xml,0.62.0
 env::unset,1.4.0
+build_machine::kernel,1.2.0

src/libtypenamespace/functions.def

@@ -3545,7 +3545,7 @@ subdir:
     - @if_found:
       - Optional: true
       - Types:
-        - list(dep)
+        - list(dep|external_program)
   - returns:
 subdir_done:
   - args:

src/libtypenamespace/methoddocs.def

@@ -13,6 +13,8 @@ Returns a more specific CPU name, such as `i686`, `amd64`, etc.
 Returns the CPU family name. [This table](https://mesonbuild.com/Reference-tables.html#cpu-families) contains all known CPU families. These are guaranteed to continue working.
 @build_machine::endian:
 Returns `'big'` on big-endian systems and `'little'` on little-endian systems.
+@build_machine::kernel:
+Returns the native kernel name. [This table](https://mesonbuild.com/Reference-tables.html#kernel-names-since-120) lists all of the currently known Kernel names.
 @build_machine::system:
 Returns the operating system name. [This table](https://mesonbuild.com/Reference-tables.html#operating-system-names) lists all of the currently known Operating System names, these are guaranteed to continue working.
 @build_tgt::extract_all_objects:

src/libtypenamespace/methods.def

@@ -36,6 +36,10 @@ build_machine::endian:
   - args:
   - returns:
     - str
+build_machine::kernel:
+  - args:
+  - returns:
+    - str
 build_machine::system:
   - args:
   - returns:
@@ -1917,6 +1921,7 @@ generator::process:
         - custom_tgt
         - custom_idx
         - generated_list
+        - exe
     - @env:
       - Optional: true
       - Types: