Check file exists in {.compile.} pragma (#21105)

* Add test

* Check file exists before adding it into compilation

* Make error message look like other error messages

i.e. following the format `error msg: file`

compiler/pragmas.nim

@@ -513,8 +513,11 @@ proc processCompile(c: PContext, n: PNode) =
     var cf = Cfile(nimname: splitFile(src).name,
                    cname: src, obj: dest, flags: {CfileFlag.External},
                    customArgs: customArgs)
-    extccomp.addExternalFileToCompile(c.config, cf)
-    recordPragma(c, it, "compile", src.string, dest.string, customArgs)
+    if not fileExists(src):
+      localError(c.config, n.info, "cannot find: " & src.string)
+    else:
+      extccomp.addExternalFileToCompile(c.config, cf)
+      recordPragma(c, it, "compile", src.string, dest.string, customArgs)
 
   proc getStrLit(c: PContext, n: PNode; i: int): string =
     n[i] = c.semConstExpr(c, n[i])

tests/pragmas/tcompile_missing_file.nim

@@ -0,0 +1,5 @@
+discard """
+  joinable: false
+  errormsg: "cannot find: noexist.c"
+"""
+{.compile: "noexist.c".}