Revert "Check prefix"

This reverts commit 1da81a0.

Author: MacDue

llvm/lib/Target/AArch64/Utils/AArch64SMEAttributes.cpp

@@ -81,10 +81,6 @@ SMEAttrs::SMEAttrs(const AttributeList &Attrs) {
 
 void SMEAttrs::addKnownFunctionAttrs(StringRef FuncName,
                                      const TargetLowering &TLI) {
-  // Skip functions that do not appear to be builtins (starting with "__").
-  if (!FuncName.starts_with('_'))
-    return;
-
   struct SMERoutineAttr {
     RTLIB::Libcall LC{RTLIB::UNKNOWN_LIBCALL};
     unsigned Attrs{SMEAttrs::Normal};