This patch eliminates the unnecessary search for various gcc installation
directories during each startup of clang.

Introduced here: http://svnweb.freebsd.org/changeset/base/259053

Index: tools/clang/lib/Driver/ToolChains.cpp
===================================================================
--- tools/clang/lib/Driver/ToolChains.cpp
+++ tools/clang/lib/Driver/ToolChains.cpp
@@ -1014,7 +1014,7 @@ static StringRef getGCCToolchainDir(const ArgList
   return GCC_INSTALL_PREFIX;
 }
 
-/// \brief Construct a GCCInstallationDetector from the driver.
+/// \brief Initialize a GCCInstallationDetector from the driver.
 ///
 /// This performs all of the autodetection and sets up the various paths.
 /// Once constructed, a GCCInstallationDetector is essentially immutable.
@@ -1023,9 +1023,9 @@ static StringRef getGCCToolchainDir(const ArgList
 /// should instead pull the target out of the driver. This is currently
 /// necessary because the driver doesn't store the final version of the target
 /// triple.
-Generic_GCC::GCCInstallationDetector::GCCInstallationDetector(
-    const Driver &D, const llvm::Triple &TargetTriple, const ArgList &Args)
-    : IsValid(false), D(D) {
+void
+Generic_GCC::GCCInstallationDetector::init(
+    const llvm::Triple &TargetTriple, const ArgList &Args) {
   llvm::Triple BiarchVariantTriple =
       TargetTriple.isArch32Bit() ? TargetTriple.get64BitArchVariant()
                                  : TargetTriple.get32BitArchVariant();
@@ -1565,7 +1565,7 @@ void Generic_GCC::GCCInstallationDetector::ScanLib
 
 Generic_GCC::Generic_GCC(const Driver &D, const llvm::Triple& Triple,
                          const ArgList &Args)
-  : ToolChain(D, Triple, Args), GCCInstallation(getDriver(), Triple, Args) {
+  : ToolChain(D, Triple, Args), GCCInstallation(getDriver()) {
   getProgramPaths().push_back(getDriver().getInstalledDir());
   if (getDriver().getInstalledDir() != getDriver().Dir)
     getProgramPaths().push_back(getDriver().Dir);
@@ -2361,6 +2361,7 @@ static StringRef getMultilibDir(const llvm::Triple
 
 Linux::Linux(const Driver &D, const llvm::Triple &Triple, const ArgList &Args)
   : Generic_ELF(D, Triple, Args) {
+  GCCInstallation.init(Triple, Args);
   llvm::Triple::ArchType Arch = Triple.getArch();
   std::string SysRoot = computeSysRoot();
 
Index: tools/clang/lib/Driver/ToolChains.h
===================================================================
--- tools/clang/lib/Driver/ToolChains.h
+++ tools/clang/lib/Driver/ToolChains.h
@@ -92,8 +92,8 @@ class LLVM_LIBRARY_VISIBILITY Generic_GCC : public
     std::set<std::string> CandidateGCCInstallPaths;
 
   public:
-    GCCInstallationDetector(const Driver &D, const llvm::Triple &TargetTriple,
-                            const llvm::opt::ArgList &Args);
+    GCCInstallationDetector(const Driver &D) : IsValid(false), D(D) {}
+    void init(const llvm::Triple &TargetTriple, const llvm::opt::ArgList &Args);
 
     /// \brief Check whether we detected a valid GCC install.
     bool isValid() const { return IsValid; }