fixes #21995: align C++ with C backend behavior for empty raise state… (#21998)

* fixes #21995: align C with C++ backend behavior for empty raise statements

* make runtime behavior match across both C and C++ backend and all exception modes

compiler/ccgstmts.nim

@@ -779,11 +779,7 @@ proc genRaiseStmt(p: BProc, t: PNode) =
   else:
     finallyActions(p)
     genLineDir(p, t)
-    # reraise the last exception:
-    if p.config.exc == excCpp:
-      line(p, cpsStmts, "throw;\n")
-    else:
-      linefmt(p, cpsStmts, "#reraiseException();$n", [])
+    linefmt(p, cpsStmts, "#reraiseException();$n", [])
   raiseInstr(p, p.s(cpsStmts))
 
 template genCaseGenericBranch(p: BProc, b: PNode, e: TLoc,

tests/ccgbugs/t21995.nim

@@ -0,0 +1,9 @@
+discard """
+    targets: "c cpp"
+    output: "Hi!"
+"""
+
+try:
+  raise
+except:
+  echo "Hi!"