[AIX] Consolidate Crt0Basename logic

[francii]

Summary

when certain flags are specified, the Crt0 object files are not linked.
However, the logic for determining which files will always run. This
patch moves that logic so that the basename is only determined if it is
needed.

[francii]

Rebase

clang/lib/Driver/ToolChains/AIX.cpp

if (IsArch32Bit) {
     CmdArgs.push_back("-bpD:0x20000000");
   } else {
     // Must be 64-bit, otherwise asserted already.
     CmdArgs.push_back("-b64");
     CmdArgs.push_back("-bpT:0x100000000");
     CmdArgs.push_back("-bpD:0x110000000");
   }
 
+  if (!Args.hasArg(options::OPT_nostdlib, options::OPT_nostartfiles,
+                   options::OPT_shared, options::OPT_r)) {
     auto getCrt0Basename = [&Args, IsArch32Bit] {
       if (Arg *A = Args.getLastArgNoClaim(options::OPT_p, options::OPT_pg)) {
         // Enable gprofiling when "-pg" is specified.
         if (A->getOption().matches(options::OPT_pg))
           return IsArch32Bit ? "gcrt0.o" : "gcrt0_64.o";
         // Enable profiling when "-p" is specified.
         return IsArch32Bit ? "mcrt0.o" : "mcrt0_64.o";
       }
       return IsArch32Bit ? "crt0.o" : "crt0_64.o";
     };
 
-  if (!Args.hasArg(options::OPT_nostdlib, options::OPT_nostartfiles,
-                   options::OPT_shared, options::OPT_r)) {
     CmdArgs.push_back(
         Args.MakeArgString(ToolChain.GetFilePath(getCrt0Basename())));
 
     CmdArgs.push_back(Args.MakeArgString(
         ToolChain.GetFilePath(IsArch32Bit ? "crti.o" : "crti_64.o")));
   }
 
   // Collect all static constructor and destructor functions in both C and CXX