Don't attempt to use mpx registers on unsupported platforms

[fjricci]

Summary

The existing cpp-level checks using PR_MPX_ENABLE_MANAGEMENT aren't sufficient,
as this isn't defined for linux kernel versions below 3.19.

[labath]

Couldn't we just update the cpp file to do

#ifndef PR_MPX_ENABLE_MANAGEMENT
return -1;
#endif

?

[fjricci]

Yeah, that works too, just wasn't sure which way was preferred.

[fjricci]

Move checks into cpp files

[labath]

I don't like either of the solutions too much, but this one is at least less code. :)

lldb/trunk/packages/Python/lldbsuite/test/functionalities/register/intel_xtended_registers/main.cpp

 //===-- main.cpp ------------------------------------------------*- C++ -*-===//
 ////
 ////                     The LLVM Compiler Infrastructure
 ////
 //// This file is distributed under the University of Illinois Open Source
 //// License. See LICENSE.TXT for details.
 ////
 ////===----------------------------------------------------------------------===//
 //
 
 #include <cpuid.h>
 #include <cstddef>
 
 int
 main(int argc, char const *argv[])
 {
+// PR_MPX_ENABLE_MANAGEMENT won't be defined on linux kernel versions below 3.19
+#ifndef PR_MPX_ENABLE_MANAGEMENT
+    return -1;
+#endif
+
     // This call returns 0 only if the CPU and the kernel support Intel(R) MPX.
     if (prctl(PR_MPX_ENABLE_MANAGEMENT, 0, 0, 0, 0) != 0)
         return -1;
 
 // Run Intel(R) MPX test code.
 #if defined(__x86_64__)
     asm("mov $16, %rax\n\t"
         "mov $9, %rdx\n\t"

lldb/trunk/packages/Python/lldbsuite/test/functionalities/register/intel_xtended_registers/mpx_bound_violation/main.cpp

 }
 
 int
 main(int argc, char const *argv[])
 {
   unsigned int rax, rbx, rcx, rdx;
   int array[5];
 
+// PR_MPX_ENABLE_MANAGEMENT won't be defined on linux kernel versions below 3.19
+#ifndef PR_MPX_ENABLE_MANAGEMENT
+    return -1;
+#endif
+
   // This call returns 0 only if the CPU and the kernel support Intel(R) MPX.
   if (prctl(PR_MPX_ENABLE_MANAGEMENT, 0, 0, 0, 0) != 0)
     return -1;
 
   violate_upper_bound(array, 5);
   violate_lower_bound(array, 5);
 
   return 0;
 }