first version of an PHP codegen

lib/system.nim

@@ -2452,14 +2452,17 @@ type
 
 when defined(JS):
   proc add*(x: var string, y: cstring) {.asmNoStackFrame.} =
-    asm """
-      var len = `x`[0].length-1;
-      for (var i = 0; i < `y`.length; ++i) {
-        `x`[0][len] = `y`.charCodeAt(i);
-        ++len;
-      }
-      `x`[0][len] = 0
-    """
+    when defined(nimphp):
+      asm """`x` .= `y`;"""
+    else:
+      asm """
+        var len = `x`[0].length-1;
+        for (var i = 0; i < `y`.length; ++i) {
+          `x`[0][len] = `y`.charCodeAt(i);
+          ++len;
+        }
+        `x`[0][len] = 0
+      """
   proc add*(x: var cstring, y: cstring) {.magic: "AppendStrStr".}
 
 elif hasAlloc: