[lldb] Fix build on older Linux kernel versions

PERF_COUNT_SW_DUMMY is introduced in Linux 3.12.

Differential Revision: https://reviews.llvm.org/D128707

lldb/source/Plugins/Process/Linux/Perf.cpp

@@ -15,6 +15,7 @@
 #include "llvm/Support/MathExtras.h"
 #include "llvm/Support/MemoryBuffer.h"
 
+#include <linux/version.h>
 #include <sys/ioctl.h>
 #include <sys/mman.h>
 #include <sys/syscall.h>
@@ -26,6 +27,7 @@ using namespace llvm;
 
 Expected<LinuxPerfZeroTscConversion>
 lldb_private::process_linux::LoadPerfTscConversionParameters() {
+#if LINUX_VERSION_CODE >= KERNEL_VERSION(3,12,0)
   lldb::pid_t pid = getpid();
   perf_event_attr attr;
   memset(&attr, 0, sizeof(attr));
@@ -55,6 +57,10 @@ lldb_private::process_linux::LoadPerfTscConversionParameters() {
                       err_cap);
     return llvm::createStringError(llvm::inconvertibleErrorCode(), err_msg);
   }
+#else
+  std::string err_msg = "PERF_COUNT_SW_DUMMY requires Linux 3.12";
+  return llvm::createStringError(llvm::inconvertibleErrorCode(), err_msg);
+#endif
 }
 
 void resource_handle::MmapDeleter::operator()(void *ptr) {