[OpenMP] Ensure offloading sections do not have SHF_ALLOC flag

[jhuber6]

Summary

We use offloading sections in the new Clang driver scheme to embed
device code into the host. We later use these sections to link the
device image, after which point they are completely unused and should
not be loaded into memory if they are still in the executable.

[JonChesterfield]

LG, thanks for including the test

llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp

static SectionKind getELFKindForNamedSection(StringRef Name, SectionKind K) {
   // section(".eh_frame") gcc will produce:
   //
   //   .section   .eh_frame,"a",@progbits
 
   if (Name == getInstrProfSectionName(IPSK_covmap, Triple::ELF,
                                       /*AddSegmentInfo=*/false) ||
       Name == getInstrProfSectionName(IPSK_covfun, Triple::ELF,
                                       /*AddSegmentInfo=*/false) ||
-      Name == ".llvmbc" || Name == ".llvmcmd")
+      Name == ".llvmbc" || Name == ".llvmcmd" ||
+      Name.startswith(".llvm.offloading."))
     return SectionKind::getMetadata();
 
   if (Name.empty() || Name[0] != '.') return K;
 
   // Default implementation based on some magic section names.
   if (Name == ".bss" ||
       Name.startswith(".bss.") ||
       Name.startswith(".gnu.linkonce.b.") ||

llvm/test/CodeGen/X86/offload_sections.ll

+; RUN: llc < %s -mtriple=x86_64-unknown-linux-gnu | FileCheck %s
+
[e-mail] = hidden constant [1 x i8] c"\00", section ".llvm.offloading.dummy"
[e-mail] = appending global [1 x i8*] [i8* getelementptr inbounds ([1 x i8], [1 x i8]* @llvm.embedded.object, i32 0, i32 0)], section "llvm.metadata"
+
+; CHECK-DAG: .section .llvm.offloading.dummy,""