[bazel] Remove hardcoded link option "-B/usr/bin"

- having this option breaks use of custom C/C++ toolchain since support binaries
  such as ld, as, etc., will incorrectly "leak" to the build machine.
- fixes issue bazelbuild#5634

Testing Done: local build of envoy. Checked that the build fails without the fix
and succeeds with the fix.
Review URL: https://reviewboard.eng.vmware.com/r/1390677/

src/test/java/com/google/devtools/build/lib/analysis/mock/MOCK_CROSSTOOL

@@ -62,7 +62,7 @@ toolchain {
   tool_path { name: "gcc" path: "/usr/bin/gcc" }
   cxx_flag: "-std=c++0x"
   linker_flag: "-lstdc++"
-  linker_flag: "-B/usr/bin/"
+  # linker_flag: "-B/usr/bin/"
 
   # TODO(bazel-team): In theory, the path here ought to exactly match the path
   # used by gcc. That works because bazel currently doesn't track files at

src/test/shell/bazel/testdata/bazel_toolchain_test_data/tools/arm_compiler/CROSSTOOL

@@ -155,8 +155,8 @@ toolchain {
   compiler_flag: "-fstack-protector"
   compiler_flag: "-Wall"
   compiler_flag: "-Wl,-z,-relro,-z,now"
-  compiler_flag: "-B/usr/bin"
-  compiler_flag: "-B/usr/bin"
+  # compiler_flag: "-B/usr/bin"
+  # compiler_flag: "-B/usr/bin"
   compiler_flag: "-Wunused-but-set-parameter"
   compiler_flag: "-Wno-free-nonheap-object"
   compiler_flag: "-fno-omit-frame-pointer"
@@ -173,8 +173,8 @@ toolchain {
   linker_flag: "-lstdc++"
   linker_flag: "-lm"
   linker_flag: "-Wl,-no-as-needed"
-  linker_flag: "-B/usr/bin"
-  linker_flag: "-B/usr/bin"
+  # linker_flag: "-B/usr/bin"
+  # linker_flag: "-B/usr/bin"
   linker_flag: "-pass-exit-codes"
   needsPic: true
   objcopy_embed_flag: "-I"

tools/cpp/CROSSTOOL

@@ -59,7 +59,7 @@ toolchain {
   tool_path { name: "gcc" path: "/usr/bin/gcc" }
   cxx_flag: "-std=c++0x"
   linker_flag: "-lstdc++"
-  linker_flag: "-B/usr/bin/"
+  # linker_flag: "-B/usr/bin/"
 
   # TODO(bazel-team): In theory, the path here ought to exactly match the path
   # used by gcc. That works because bazel currently doesn't track files at
@@ -271,7 +271,7 @@ toolchain {
   tool_path { name: "gcc" path: "/usr/bin/clang" }
   cxx_flag: "-std=c++0x"
   linker_flag: "-lstdc++"
-  linker_flag: "-B/usr/bin/"
+  # linker_flag: "-B/usr/bin/"
 
   # TODO(bazel-team): In theory, the path here ought to exactly match the path
   # used by gcc. That works because bazel currently doesn't track files at

tools/cpp/unix_cc_configure.bzl

@@ -283,7 +283,7 @@ def _crosstool_content(repository_ctx, cc, cpu_value, darwin):
                 "-headerpad_max_install_names",
             ] if darwin else bin_search_flag + [
                 # Always have -B/usr/bin, see https://github.com/bazelbuild/bazel/issues/760.
-                "-B/usr/bin",
+                # "-B/usr/bin",
                 # Gold linker only? Can we enable this by default?
                 # "-Wl,--warn-execstack",
                 # "-Wl,--detect-odr-violations"
@@ -320,7 +320,7 @@ def _crosstool_content(repository_ctx, cc, cpu_value, darwin):
             _add_compiler_option_if_supported(repository_ctx, cc, "-Wself-assign")
         ) if darwin else bin_search_flag + [
             # Always have -B/usr/bin, see https://github.com/bazelbuild/bazel/issues/760.
-            "-B/usr/bin",
+            # "-B/usr/bin",
         ]) + (
             # Disable problematic warnings.
             _add_compiler_option_if_supported(repository_ctx, cc, "-Wunused-but-set-parameter") +