diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -72,6 +72,10 @@
 -----------------------
 
 - -Wshadow now also checks for shadowed structured bindings
+- ``-B <prefix>`` (when ``<prefix>>`` is a directory) used to detect GCC
+  installations under ``<prefix>``.  This behavior is incompatible with GCC,
+  causes interop issues with ``--gcc-toolchain``, and is thus dropped. Specify
+  ``--gcc-toolchain=<prefix>`` instead.
 
 Removed Compiler Flags
 -------------------------
diff --git a/clang/lib/Driver/ToolChains/Gnu.cpp b/clang/lib/Driver/ToolChains/Gnu.cpp
--- a/clang/lib/Driver/ToolChains/Gnu.cpp
+++ b/clang/lib/Driver/ToolChains/Gnu.cpp
@@ -1907,8 +1907,9 @@
                            CandidateBiarchTripleAliases);
 
   // Compute the set of prefixes for our search.
-  SmallVector<std::string, 8> Prefixes(D.PrefixDirs.begin(),
-                                       D.PrefixDirs.end());
+  SmallVector<std::string, 8> Prefixes;
+  if (TargetTriple.isAndroid())
+    Prefixes.assign(D.PrefixDirs.begin(), D.PrefixDirs.end());
 
   StringRef GCCToolchainDir = getGCCToolchainDir(Args, D.SysRoot);
   if (GCCToolchainDir != "") {
diff --git a/clang/test/Driver/gcc-toolchain.cpp b/clang/test/Driver/gcc-toolchain.cpp
--- a/clang/test/Driver/gcc-toolchain.cpp
+++ b/clang/test/Driver/gcc-toolchain.cpp
@@ -29,3 +29,14 @@
 // CHECK: "{{[^"]*}}/usr/lib/i386-linux-gnu/gcc/i686-linux-gnu/4.5{{/|\\\\}}crtbegin.o"
 // CHECK: "-L[[TOOLCHAIN]]/usr/lib/i386-linux-gnu/gcc/i686-linux-gnu/4.5"
 // CHECK: "-L[[TOOLCHAIN]]/usr/lib/i386-linux-gnu/gcc/i686-linux-gnu/4.5/../../../.."
+
+/// Test we don't detect GCC installation under -B.
+// RUN: %clangxx -no-canonical-prefixes %s -### -o %t 2>&1 \
+// RUN:   --target=aarch64-suse-linux --gcc-toolchain=%S/Inputs/opensuse_42.2_aarch64_tree/usr | \
+// RUN:   FileCheck %s --check-prefix=AARCH64
+// RUN: %clangxx -no-canonical-prefixes %s -### -o %t 2>&1 \
+// RUN:   --target=aarch64-suse-linux -B%S/Inputs/opensuse_42.2_aarch64_tree/usr | \
+// RUN:   FileCheck %s --check-prefix=NO_AARCH64
+
+// AARCH64:        Inputs{{[^"]+}}aarch64-suse-linux/{{[^"]+}}crt1.o"
+// NO_AARCH64-NOT: Inputs{{[^"]+}}aarch64-suse-linux/{{[^"]+}}crt1.o"