{.compilerproc, importc.} doesn't honor importc with nim cpp

[timotheecour]

While working on #15827 I encountered this.

{.compilerproc, importc.} has C++ linkage with nim cpp

workaround

when defined cpp:
  {.pragma: nimexectrace_internal, compilerproc, importc, codegenDecl: "NIM_EXTERNC $1 $2$3".}
else:
  {.pragma: nimexectrace_internal, compilerproc, importc.}
proc nimExecTraceEnter(procIndex: int, name: cstring) {.nimexectrace_internal.}

Additional Information

1.5.1 6b3c77e
D20210805T114254