MSP430: Move __mspabi_mpyll calling conv config to tablegen (#153988)

There are several libcall choices for MUL_I64 which depend on the
subtarget, but this is the base case. The manual custom ISelLowering
is still overriding the decision until we have a way to control
lowering choices, but we can still get the calling convention
set for now.

llvm/include/llvm/IR/RuntimeLibcalls.td

diff --git a/llvm/include/llvm/IR/RuntimeLibcalls.td b/llvm/include/llvm/IR/RuntimeLibcalls.td
index 9626004..dec7376 100644
--- a/llvm/include/llvm/IR/RuntimeLibcalls.td
+++ b/llvm/include/llvm/IR/RuntimeLibcalls.td
@@ -2094,6 +2094,9 @@
       __mspabi_remul,
       LibcallsWithCC<(add __mspabi_remull), MSP430_BUILTIN>,
 
+      // May not be used depending on subtarget
+      LibcallsWithCC<(add __mspabi_mpyll), MSP430_BUILTIN>,
+
       // Bitwise Operations - EABI Table 10
       // TODO: __mspabi_[srli/srai/slli] ARE implemented in libgcc
       __mspabi_srll,

llvm/lib/IR/RuntimeLibcalls.cpp

diff --git a/llvm/lib/IR/RuntimeLibcalls.cpp b/llvm/lib/IR/RuntimeLibcalls.cpp
index 88cb192..09fb78e 100644
--- a/llvm/lib/IR/RuntimeLibcalls.cpp
+++ b/llvm/lib/IR/RuntimeLibcalls.cpp
@@ -54,11 +54,6 @@
 
     return;
   }
-
-  if (TT.getArch() == Triple::ArchType::msp430) {
-    setLibcallImplCallingConv(RTLIB::__mspabi_mpyll,
-                              CallingConv::MSP430_BUILTIN);
-  }
 }
 
 LLVM_ATTRIBUTE_ALWAYS_INLINE