docs: Fix broken anchor links [skip ci]

Apparently anchor links are case-sensitive and needs to be lowercase in hotdoc.
Prior to this change the anchor links were uppercase so the link did not refer to the anchor tag.

Likely that there are more occurrences around the docs than this, have not looked.

docs/markdown/Builtin-options.md

@@ -57,7 +57,7 @@ particularly the paths section may be necessary.
 ### Core options
 
 Options that are labeled "per machine" in the table are set per machine. See
-the [specifying options per machine](#Specifying-options-per-machine) section
+the [specifying options per machine](#specifying-options-per-machine) section
 for details.
 
 | Option                               | Default value | Description                                                    | Is per machine | Is per subproject |
@@ -185,7 +185,7 @@ argument forms, but the libraries are: kernel32, user32, gdi32, winspool,
 shell32, ole32, oleaut32, uuid, comdlg32, advapi32.
 
 All these `<lang>_*` options are specified per machine. See below in the
-[specifying options per machine](#Specifying-options-per-machine) section on
+[specifying options per machine](#specifying-options-per-machine) section on
 how to do this in cross builds.
 
 When using MSVC, `cpp_eh=none` will result in no exception flags being passed,