[Driver] -p: change from unused warning to error for most targets

[MaskRay]

Summary

AIX and OpenBSD seem to use -p. For most targets (at least FreeBSD and Linux),
-p is legacy (GCC freebsd has a warning). We don't want the uses to grow, so
making -p an alias for -pg is not recommended. I think the uses are small.

[MaskRay]

Ping

[mgorny]

LGTM

[MaskRay]

Thanks! I think this is better landing before AIX -p patches for clarity, so I am landing it now...

clang/docs/ReleaseNotes.rst

 - Clang's resource dir used to include the full clang version. It will now
   include only the major version. The new resource directory is
   ``$prefix/lib/clang/$CLANG_MAJOR_VERSION`` and can be queried using
   ``clang -print-resource-dir``, just like before.
 
 - To match GCC, ``__ppc64__`` is no longer defined on PowerPC64 targets. Use
   ``__powerpc64__`` instead.
 
+- ``-p`` is rejected for all targets which are not AIX or OpenBSD. ``-p`` led
+  to an ``-Wunused-command-line-argument`` warning in previous releases.
+
 What's New in Clang |release|?
 ==============================
 Some of the major new features and improvements to Clang are listed
 here. Generic improvements to Clang as a whole or to its underlying
 infrastructure are described first, followed by language-specific
 sections with improvements to Clang's support for those languages.
 
 Major New Features

clang/lib/Driver/ToolChains/Clang.cpp

if (TC.SupportsProfiling()) {
     if (Arg *A = Args.getLastArg(options::OPT_mrecord_mcount)) {
       if (Arch == llvm::Triple::systemz)
         A->render(Args, CmdArgs);
       else
         D.Diag(diag::err_drv_unsupported_opt_for_target)
             << A->getAsString(Args) << TripleStr;
     }
   }
+  if (Arg *A = Args.getLastArgNoClaim(options::OPT_p)) {
+    if (!TC.getTriple().isOSAIX() && !TC.getTriple().isOSOpenBSD()) {
+      D.Diag(diag::err_drv_unsupported_opt_for_target)
+          << A->getAsString(Args) << TripleStr;
+    }
+  }
 
   if (Args.getLastArg(options::OPT_fapple_kext) ||
       (Args.hasArg(options::OPT_mkernel) && types::isCXX(InputType)))
     CmdArgs.push_back("-fapple-kext");
 
   Args.AddLastArg(CmdArgs, options::OPT_altivec_src_compat);
   Args.AddLastArg(CmdArgs, options::OPT_flax_vector_conversions_EQ);
   Args.AddLastArg(CmdArgs, options::OPT_fobjc_sender_dependent_dispatch);

clang/test/Driver/p.c

+/// For most targets -p is legacy. We used to report -Wunused-command-line-argument.
+// RUN: %clang -### --target=x86_64-unknown-linux-gnu -c -p %s 2>&1 | FileCheck %s --check-prefix=ERR
+
+// RUN: %clang -### --target=x86_64-unknown-openbsd -c -p %s 2>&1 | FileCheck %s --implicit-check-not=error:
+// RUN: %clang -### --target=powerpc64-ibm-aix -c -p %s 2>&1 | FileCheck %s --implicit-check-not=error:
+
+// ERR: error: unsupported option '-p' for target {{.*}}