Fix ComputeSupportExeDirectory for Linux (merge with Android).

[chaoren]

Summary

ComputeSupportExeDirectory relied on ComputeSharedLibraryDirectory which was
not always reliable. Using procfs seems to be the best way to deal with it on
Linux (since it's already done on Android, might as well merge it).

[ovyalov]

Looks good.

[clayborg]

lgtm

include/lldb/Host/android/HostInfoAndroid.h

class HostInfoAndroid : public HostInfoLinux
     friend class HostInfoBase;
 
   public:
     static FileSpec GetDefaultShell();
     static FileSpec ResolveLibraryPath (const std::string& path, const ArchSpec& arch);
 
   protected:
     static void ComputeHostArchitectureSupport(ArchSpec &arch_32, ArchSpec &arch_64);
-    static bool ComputeSupportExeDirectory(FileSpec &file_spec);
 };
 
 } // end of namespace lldb_private
 
 #endif // #ifndef lldb_Host_android_HostInfoAndroid_h_

include/lldb/Host/linux/HostInfoLinux.h

public:
 
     static bool GetOSVersion(uint32_t &major, uint32_t &minor, uint32_t &update);
     static bool GetOSBuildString(std::string &s);
     static bool GetOSKernelDescription(std::string &s);
     static llvm::StringRef GetDistributionId();
     static FileSpec GetProgramFileSpec();
 
   protected:
-    static bool ComputeSharedLibraryDirectory(FileSpec &file_spec);
+    static bool ComputeSupportExeDirectory(FileSpec &file_spec);
     static bool ComputeSystemPluginsDirectory(FileSpec &file_spec);
     static bool ComputeUserPluginsDirectory(FileSpec &file_spec);
     static void ComputeHostArchitectureSupport(ArchSpec &arch_32, ArchSpec &arch_64);
 };
 }
 
 #endif

source/Host/android/HostInfoAndroid.cpp

if (arch_32.IsValid())
         arch_32.GetTriple().setEnvironment(llvm::Triple::Android);
     }
     if (arch_64.IsValid())
     {
         arch_64.GetTriple().setEnvironment(llvm::Triple::Android);
     }
 }
 
-bool
-HostInfoAndroid::ComputeSupportExeDirectory(FileSpec &file_spec)
-{
-    file_spec.GetDirectory() = HostInfoLinux::GetProgramFileSpec().GetDirectory();
-    return (bool)file_spec.GetDirectory();
-}
-
 FileSpec
 HostInfoAndroid::GetDefaultShell()
 {
     return FileSpec("/system/bin/sh", false);
 }
 
 FileSpec
 HostInfoAndroid::ResolveLibraryPath(const std::string& module_path, const ArchSpec& arch)

source/Host/linux/HostInfoLinux.cpp

if (!g_program_filespec)
             g_program_filespec.SetFile(exe_path, false);
         }
     }
 
     return g_program_filespec;
 }
 
 bool
-HostInfoLinux::ComputeSharedLibraryDirectory(FileSpec &file_spec)
+HostInfoLinux::ComputeSupportExeDirectory(FileSpec &file_spec)
 {
-    if (HostInfoPosix::ComputeSharedLibraryDirectory(file_spec))
-        return true;
     file_spec.GetDirectory() = GetProgramFileSpec().GetDirectory();
-    return (bool)file_spec.GetDirectory();
+    return static_cast<bool>(file_spec.GetDirectory());
 }
 
 bool
 HostInfoLinux::ComputeSystemPluginsDirectory(FileSpec &file_spec)
 {
     FileSpec temp_file("/usr/lib/lldb", true);
     file_spec.GetDirectory().SetCString(temp_file.GetPath().c_str());
     return true;