Revert "Driver: Don't look for libc++ headers in the install directory on Android."

This reverts commit 198fbcb.

This breaks Fedora 31.

Author: davezarzycki

clang/lib/Driver/ToolChains/Linux.cpp

@@ -888,25 +888,20 @@ static std::string DetectLibcxxIncludePath(llvm::vfs::FileSystem &vfs,
 void Linux::addLibCxxIncludePaths(const llvm::opt::ArgList &DriverArgs,
                                   llvm::opt::ArgStringList &CC1Args) const {
   const std::string& SysRoot = computeSysRoot();
-  auto AddIncludePath = [&](std::string Path) {
-    std::string IncludePath = DetectLibcxxIncludePath(getVFS(), Path);
+  const std::string LibCXXIncludePathCandidates[] = {
+      DetectLibcxxIncludePath(getVFS(), getDriver().Dir + "/../include/c++"),
+      // If this is a development, non-installed, clang, libcxx will
+      // not be found at ../include/c++ but it likely to be found at
+      // one of the following two locations:
+      DetectLibcxxIncludePath(getVFS(), SysRoot + "/usr/local/include/c++"),
+      DetectLibcxxIncludePath(getVFS(), SysRoot + "/usr/include/c++") };
+  for (const auto &IncludePath : LibCXXIncludePathCandidates) {
     if (IncludePath.empty() || !getVFS().exists(IncludePath))
-      return false;
+      continue;
+    // Use the first candidate that exists.
     addSystemInclude(DriverArgs, CC1Args, IncludePath);
-    return true;
-  };
-  // Android never uses the libc++ headers installed alongside the toolchain,
-  // which are generally incompatible with the NDK libraries anyway.
-  if (!getTriple().isAndroid())
-    if (AddIncludePath(getDriver().Dir + "/../include/c++"))
-      return;
-  // If this is a development, non-installed, clang, libcxx will
-  // not be found at ../include/c++ but it likely to be found at
-  // one of the following two locations:
-  if (AddIncludePath(SysRoot + "/usr/local/include/c++"))
-    return;
-  if (AddIncludePath(SysRoot + "/usr/include/c++"))
     return;
+  }
 }
 
 void Linux::addLibStdCxxIncludePaths(const llvm::opt::ArgList &DriverArgs,

clang/test/Driver/android-no-installed-libcxx.cpp

@@ -6,7 +6,7 @@
 // By default, we should search for libc++ next to the driver.
 // RUN: mkdir -p %t/bin
 // RUN: mkdir -p %t/include/c++/v1
-// RUN: %clang -target aarch64-linux-gnu -ccc-install-dir %t/bin \
+// RUN: %clang -target aarch64-linux-android -ccc-install-dir %t/bin \
 // RUN:   -stdlib=libc++ -fsyntax-only %s -### 2>&1 | \
 // RUN:   FileCheck -check-prefix=LIBCXX %s
 // RUN: %clang -target x86_64-apple-darwin -ccc-install-dir %t/bin \
@@ -16,7 +16,7 @@
 // LIBCXX: "-internal-isystem" "[[INSTALLDIR]]/../include/c++/v1"
 
 // Passing -stdlib++-isystem should suppress the default search.
-// RUN: %clang -target aarch64-linux-gnu -ccc-install-dir %t/bin \
+// RUN: %clang -target aarch64-linux-android -ccc-install-dir %t/bin \
 // RUN:   -stdlib++-isystem /tmp/foo -stdlib++-isystem /tmp/bar -stdlib=libc++ \
 // RUN:   -fsyntax-only %s -### 2>&1 | FileCheck -check-prefix=NODEFAULT %s
 // RUN: %clang -target x86_64-apple-darwin -ccc-install-dir %t/bin \
@@ -26,7 +26,7 @@
 // NODEFAULT-NOT: "-internal-isystem" "[[INSTALLDIR]]/../include/c++/v1"
 
 // And we should add it as an -internal-isystem.
-// RUN: %clang -target aarch64-linux-gnu -ccc-install-dir %t/bin \
+// RUN: %clang -target aarch64-linux-android -ccc-install-dir %t/bin \
 // RUN:   -stdlib++-isystem /tmp/foo -stdlib++-isystem /tmp/bar -stdlib=libc++ \
 // RUN:   -fsyntax-only %s -### 2>&1 | FileCheck -check-prefix=INCPATH %s
 // RUN: %clang -target x86_64-apple-darwin -ccc-install-dir %t/bin \
@@ -35,7 +35,7 @@
 // INCPATH: "-internal-isystem" "/tmp/foo" "-internal-isystem" "/tmp/bar"
 
 // We shouldn't pass the -stdlib++-isystem to cc1.
-// RUN: %clang -target aarch64-linux-gnu -ccc-install-dir %t/bin \
+// RUN: %clang -target aarch64-linux-android -ccc-install-dir %t/bin \
 // RUN:   -stdlib++-isystem /tmp -stdlib=libc++ -fsyntax-only %s -### 2>&1 | \
 // RUN:   FileCheck -check-prefix=NOCC1 %s
 // RUN: %clang -target x86_64-apple-darwin -ccc-install-dir %t/bin \
@@ -44,7 +44,7 @@
 // NOCC1-NOT: "-stdlib++-isystem" "/tmp"
 
 // It should respect -nostdinc++.
-// RUN: %clang -target aarch64-linux-gnu -ccc-install-dir %t/bin \
+// RUN: %clang -target aarch64-linux-android -ccc-install-dir %t/bin \
 // RUN:   -stdlib++-isystem /tmp/foo -stdlib++-isystem /tmp/bar -nostdinc++ \
 // RUN:   -fsyntax-only %s -### 2>&1 | FileCheck -check-prefix=NOSTDINCXX %s
 // RUN: %clang -target x86_64-apple-darwin -ccc-install-dir %t/bin \