LSP reports "'stdio.h' file not found'

[Littlechay]

Me again with another silly questions....

I have installed the lsp module (I installed all the modules using the link on the textadept page), and configured it for ansi_C like this:
-- lsp stuff

local lsp = require('lsp')

lsp.server_commands.cpp = 'clangd'
lsp.server_commands.ansi_c = 'clangd'
lsp.server_commands.go = 'gopls'

But I get this error and further down more warning such as printf undeclared library function etc..

So my question is: How do I tell the language server where the standard header files are located? They are in /usr/include .

Edit: I should also add that although math.h does not show a warning, as can be seen in the screenshot, that in the code I get warnings for math functions stating that math.h is not included.

The project compiles and runs just fine.

[orbitalquark]

clangd usually needs a "compile_commands.json" file or similar to provide context: https://clangd.llvm.org/design/compile-commands. You shouldn't have to pass any flags or configuration options to clangd.