fixes #10299 (#11324)

compiler/cgen.nim

@@ -1837,9 +1837,9 @@ proc writeHeader(m: BModule) =
 
 proc getCFile(m: BModule): AbsoluteFile =
   let ext =
-      if m.compileToCpp: ".cpp"
-      elif m.config.cmd == cmdCompileToOC or sfCompileToObjC in m.module.flags: ".m"
-      else: ".c"
+      if m.compileToCpp: ".nim.cpp"
+      elif m.config.cmd == cmdCompileToOC or sfCompileToObjC in m.module.flags: ".nim.m"
+      else: ".nim.c"
   result = changeFileExt(completeCFilePath(m.config, withPackageName(m.config, m.cfilename)), ext)
 
 when false:

testament/specs.nim

@@ -78,7 +78,7 @@ proc getCmd*(s: TSpec): string =
     result = s.cmd
 
 const
-  targetToExt*: array[TTarget, string] = ["c", "cpp", "m", "js"]
+  targetToExt*: array[TTarget, string] = ["nim.c", "nim.cpp", "nim.m", "js"]
   targetToCmd*: array[TTarget, string] = ["c", "cpp", "objc", "js"]
 
 when not declared(parseCfgBool):

tests/compilepragma/test.c

@@ -0,0 +1,3 @@
+int foo(int a, int b) {
+  return a+b;
+}

tests/compilepragma/test.nim

@@ -0,0 +1,10 @@
+discard """
+  output: '''44'''
+  joinable: "false"
+"""
+
+{.compile: "test.c".}
+
+proc foo(a, b: cint): cint {.importc: "foo", cdecl.}
+
+echo foo(40, 4)