docs: Clarify compiler.cmd_array() (#8454)

Make it easier to understand that this array contains the compiler
command, not arguments to it, and may only have one element.

docs/markdown/Reference-manual.md

@@ -2236,8 +2236,7 @@ the following methods:
   the positional argument, you can specify external dependencies to
   use with `dependencies` keyword argument.
 
-- `cmd_array()`: returns an array containing the command arguments for
-  the current compiler.
+- `cmd_array()`: returns an array containing the command(s) for the compiler.
 
 - `compiles(code)`: returns true if the code fragment given in the
   positional argument compiles, you can specify external dependencies