Fix failures in AllocationTests/MappedMemoryTest.* on aarch64:

    Failing Tests (8):
        LLVM-Unit :: Support/./SupportTests/AllocationTests/MappedMemoryTest.AllocAndRelease/3
        LLVM-Unit :: Support/./SupportTests/AllocationTests/MappedMemoryTest.DuplicateNear/3
        LLVM-Unit :: Support/./SupportTests/AllocationTests/MappedMemoryTest.EnabledWrite/3
        LLVM-Unit :: Support/./SupportTests/AllocationTests/MappedMemoryTest.MultipleAllocAndRelease/3
        LLVM-Unit :: Support/./SupportTests/AllocationTests/MappedMemoryTest.SuccessiveNear/3
        LLVM-Unit :: Support/./SupportTests/AllocationTests/MappedMemoryTest.UnalignedNear/3
        LLVM-Unit :: Support/./SupportTests/AllocationTests/MappedMemoryTest.ZeroNear/3
        LLVM-Unit :: Support/./SupportTests/AllocationTests/MappedMemoryTest.ZeroSizeNear/3

Upstream-Issue: https://bugs.llvm.org/show_bug.cgi?id=14278#c10

--- a/llvm/lib/Support/Unix/Memory.inc
+++ b/llvm/lib/Support/Unix/Memory.inc
@@ -58,7 +58,7 @@
     return PROT_READ | PROT_WRITE | PROT_EXEC;
   case llvm::sys::Memory::MF_EXEC:
 #if (defined(__FreeBSD__) || defined(__POWERPC__) || defined (__ppc__) || \
-     defined(_POWER) || defined(_ARCH_PPC))
+     defined(_POWER) || defined(_ARCH_PPC) || (defined(__linux__) && defined(__aarch64__)))
     // On PowerPC, having an executable page that has no read permission
     // can have unintended consequences.  The function InvalidateInstruction-
     // Cache uses instructions dcbf and icbi, both of which are treated by