make goto based exceptions available for 'nim cpp' (#13244)

* make goto based exceptions available for 'nim cpp'
* optimize seq.add to be comparable to C++'s emplace_back

lib/system/excpt.nim

@@ -61,7 +61,7 @@ var
   currException {.threadvar.}: ref Exception
   gcFramePtr {.threadvar.}: GcFrame
 
-when defined(cpp) and not defined(noCppExceptions):
+when defined(cpp) and not defined(noCppExceptions) and not gotoBasedExceptions:
   var
     raiseCounter {.threadvar.}: uint
 
@@ -410,7 +410,7 @@ proc reportUnhandledError(e: ref Exception) {.nodestroy.} =
     discard()
 
 proc nimLeaveFinally() {.compilerRtl.} =
-  when defined(cpp) and not defined(noCppExceptions):
+  when defined(cpp) and not defined(noCppExceptions) and not gotoBasedExceptions:
     {.emit: "throw;".}
   else:
     if excHandler != nil:
@@ -439,7 +439,7 @@ proc raiseExceptionAux(e: sink(ref Exception)) {.nodestroy.} =
     if not localRaiseHook(e): return
   if globalRaiseHook != nil:
     if not globalRaiseHook(e): return
-  when defined(cpp) and not defined(noCppExceptions):
+  when defined(cpp) and not defined(noCppExceptions) and not gotoBasedExceptions:
     if e == currException:
       {.emit: "throw;".}
     else:
@@ -544,7 +544,7 @@ proc nimFrame(s: PFrame) {.compilerRtl, inl, raises: [].} =
   framePtr = s
   if s.calldepth == nimCallDepthLimit: callDepthLimitReached()
 
-when defined(cpp) and appType != "lib" and
+when defined(cpp) and appType != "lib" and not gotoBasedExceptions and
     not defined(js) and not defined(nimscript) and
     hostOS != "standalone" and not defined(noCppExceptions):
 

lib/system/memtracker.nim

@@ -80,7 +80,7 @@ proc addEntry(entry: LogEntry) =
       #inc gLog.count
       #gLog.disabled = false
 
-proc memTrackerWrite(address: pointer; size: int; file: cstring; line: int) {.compilerProc.} =
+proc memTrackerWrite(address: pointer; size: int; file: cstring; line: int) {.compilerproc.} =
   addEntry LogEntry(op: "write", address: address,
       size: size, file: file, line: line, thread: myThreadId())
 

lib/system/seqs_v2.nim

@@ -92,7 +92,7 @@ proc grow*[T](x: var seq[T]; newLen: Natural; value: T) =
   for i in oldLen .. newLen-1:
     xu.p.data[i] = value
 
-proc add*[T](x: var seq[T]; value: sink T) {.magic: "AppendSeqElem", noSideEffect.} =
+proc add*[T](x: var seq[T]; value: sink T) {.magic: "AppendSeqElem", noSideEffect, nodestroy.} =
   ## Generic proc for adding a data item `y` to a container `x`.
   ##
   ## For containers that have an order, `add` means *append*. New generic
@@ -104,6 +104,10 @@ proc add*[T](x: var seq[T]; value: sink T) {.magic: "AppendSeqElem", noSideEffec
   if xu.p == nil or xu.p.cap < oldLen+1:
     xu.p = cast[typeof(xu.p)](prepareSeqAdd(oldLen, xu.p, 1, sizeof(T)))
   xu.len = oldLen+1
+  # .nodestroy means `xu.p.data[oldLen] = value` is compiled into a
+  # copyMem(). This is fine as know by construction that
+  # in `xu.p.data[oldLen]` there is nothing to destroy.
+  # We also save the `wasMoved + destroy` pair for the sink parameter.
   xu.p.data[oldLen] = value
 
 proc setLen[T](s: var seq[T], newlen: Natural) =