[LangRef] Clarify that noimplicitfloat disables all implicit vectors not just floating point.

[fhahn]

LGTM together with D134084, thanks!

llvm/docs/LangRef.rst

``nofree``
     pointers cannot be freed by the function.
 
     A ``nofree`` function is explicitly allowed to free memory which it
     allocated or (if not ``nosync``) arrange for another thread to free
     memory on it's behalf.  As a result, perhaps surprisingly, a ``nofree``
     function can return a pointer to a previously deallocated memory object.
 ``noimplicitfloat``
     Disallows implicit floating-point code. This inhibits optimizations that
-    use floating-point code and floating-point/SIMD/vector registers for
-    operations that are not nominally floating-point. LLVM instructions that
-    perform floating-point operations or require access to floating-point
-    registers may still cause floating-point code to be generated.
+    use floating-point code and floating-point registers for operations that are
+    not nominally floating-point. LLVM instructions that perform floating-point
+    operations or require access to floating-point registers may still cause
+    floating-point code to be generated.
+
+    Also inhibits optimizations that create SIMD/vector code and registers from
+    scalar code such as vectorization or memcpy/memset optimization. This
+    includes integer vectors. Vector instructions present in IR may still cause
+    vector code to be generated.
 ``noinline``
     This attribute indicates that the inliner should never inline this
     function in any situation. This attribute may not be used together
     with the ``alwaysinline`` attribute.
 ``nomerge``
     This attribute indicates that calls to this function should never be merged
     during optimization. For example, it will prevent tail merging otherwise
     identical code sequences that raise an exception or terminate the program.