Fix RyuJIT/x86 fgMorphMultiregStructArg NYI

The code leading to the fgMorphMultiregStructArg NYI shouldn't have been taken for x86.
In fgMorphArgs, I put the setting of `hasMultiregStructArgs = true` in one case under `#ifdef`.

Disable tests failing with a newly exposed assert, `'isPhiDefn || type != TYP_STRUCT'`,
tracked by #6180.

I also fixed a number of asserts on strings that would never fail the way they were
written -- `assert("string")` instead of `assert(!"string")` -- and fixed some typos/grammar.

1 files changed, 2 insertions, 2 deletions

diff --git a/src/jit/simdcodegenxarch.cpp b/src/jit/simdcodegenxarch.cpp
index f512b46a19..f6218bdee2 100644
--- a/src/jit/simdcodegenxarch.cpp
+++ b/src/jit/simdcodegenxarch.cpp
@@ -1233,7 +1233,7 @@ CodeGen::genSIMDIntrinsicRelOp(GenTreeSIMD* simdNode)
         break;
 
     default:
-        noway_assert("Unimplemented SIMD relational operation.");
+        noway_assert(!"Unimplemented SIMD relational operation.");
         unreached();
     }
 
@@ -2147,7 +2147,7 @@ CodeGen::genSIMDIntrinsic(GenTreeSIMD* simdNode)
         break;
 
     default:
-        noway_assert("Unimplemented SIMD intrinsic.");
+        noway_assert(!"Unimplemented SIMD intrinsic.");
         unreached();
     }
 }