runtime use of compileTime proc should error immediately, not at codegen

[timotheecour]

proc fun(){.compileTime.} =
  echo "step2"

static: echo "step1"

fun() # user error: should've been: `static: fun()`

static: echo "step3 (with side effects) that expects step2 to run before"

nim c main.nim prints:

step1
step3 (with side effects) that expects step2 to run before
/Users/timothee/git_clone/nim/timn/tests/nim/all/t0176.nim(8, 1) template/generic instantiation from here
/Users/timothee/git_clone/nim/timn/tests/nim/all/t0176.nim(10, 1) Error: request to generate code for .compileTime proc: fun
  fun() # user error: should've been: `static: fun()`
  ^

expected output:

step1
/Users/timothee/git_clone/nim/timn/tests/nim/all/t0176.nim(8, 1) template/generic instantiation from here
/Users/timothee/git_clone/nim/timn/tests/nim/all/t0176.nim(10, 1) Error: compileTime proc: fun used in a run time context # <= msg can be something like this ****
  fun() # user error: should've been: `static: fun()`
  ^

ie, compilation should stop earlier and not keep going past the point where fun() is used in a non CT context

other confusing example

I faced a situation (nimterop/nimterop#102 (comment)) where the error Error: request to generate code for .compileTime proc: fun was never printed because "step 3" errored as a result of "step 2" not being run at CT; in more complex cases than above simplified example this is hard to diagnose.

[liquidev]

I agree that the error message should be changed, it was quite confusing when I stumbled onto it the first time. Perhaps attempt to use compileTime proc 'fun' at runtime would be a bit more clear?