Sema: add error for non-comptime param in comptime func

Adds error for taking a non comptime parameter in a function returning a
comptime-only type but not when that type is dependent on a parameter.

Co-authored-by: Veikka Tuominen <git@vexu.eu>

lib/std/io/bit_reader.zig

@@ -7,7 +7,7 @@ const meta = std.meta;
 const math = std.math;
 
 /// Creates a stream which allows for reading bit fields from another stream
-pub fn BitReader(endian: std.builtin.Endian, comptime ReaderType: type) type {
+pub fn BitReader(comptime endian: std.builtin.Endian, comptime ReaderType: type) type {
     return struct {
         forward_reader: ReaderType,
         bit_buffer: u7,