fixes #23114; Nim v2 regression emit / asm var param dereference inconsistency (#24547)

fixes #23114

As in https://github.com/nim-lang/Nim/pull/22074, expressions in
bracketed emit are strictly typechecked, this PR applies the same check
for symbols in asm statements in order to keep them consistent.

tests/compiler/tasm2.nim

@@ -0,0 +1,54 @@
+discard """
+  targets: "c cpp"
+  disabled: "arm64"
+"""
+
+import std/strutils
+
+block: # bug #23114
+  func ccopy_x86_asm(ctl: uint64, x: var uint64, y: uint64) =
+    asm """
+      testq %[ctl], %[ctl]
+      cmovnzq %[y], %[x]
+      : [x] "+r" (`x`)
+      : [ctl] "r" (`ctl`), [y] "r" (`y`)
+      : "cc"
+    """
+
+  func ccopy_x86_emit(ctl: uint64, x: var uint64, y: uint64) =
+    {.emit:[
+      """
+      asm volatile(
+        "testq %[ctl], %[ctl]\n"
+        "cmovnzq %[y], %[x]\n"
+        : [x] "+r" (""", x, """)
+        : [ctl] "r" (""", ctl, """), [y] "r" (""", y, """)
+        : "cc"
+      );"""].}
+
+
+  let x = 0x1111111'u64
+  let y = 0xFFFFFFF'u64
+
+  block:
+    let ctl = 1'u64
+    var a0 = x
+    ctl.ccopy_x86_asm(a0, y)
+
+    var a1 = x
+    ctl.ccopy_x86_emit(a1, y)
+
+    doAssert a0.toHex() == "000000000FFFFFFF"
+    doAssert a0 == a1
+
+  block:
+    let ctl = 0'u64
+    var a0 = x
+    ctl.ccopy_x86_asm(a0, y)
+
+    var a1 = x
+    ctl.ccopy_x86_emit(a1, y)
+
+    doAssert a0.toHex() == "0000000001111111"
+    doAssert a0 == a1
+

tests/config.nims

@@ -38,6 +38,7 @@ switch("define", "nimPreviewHashRef")
 switch("define", "nimPreviewRangeDefault")
 switch("define", "nimPreviewNonVarDestructor")
 switch("define", "nimPreviewCheckedClose")
+switch("define", "nimPreviewAsmSemSymbol")
 
 switch("warningAserror", "UnnamedBreak")
 when not defined(testsConciseTypeMismatch):