Patch to fix bazel rule issues for boost library in ARM (aarch64)

rules_boost-context-thread-arm64.patch

This patch fixes ARM (aarch64) bazel build rules for boost libraries when
building ray as discussed in this issue - https://github.com/ray-project/ray/issues/7184.
Patch v2 by Abishek Muthian (@heavyinfo).
--- BUILD.boost	2020-02-23 09:03:02.937872389 +0530
+++ BUILD.boost	2020-02-26 07:18:26.287128627 +0530
@@ -49,6 +49,15 @@
 )
 
 config_setting(
+    name = "linux_aarch64",
+    constraint_values = [
+        "@bazel_tools//platforms:linux",
+        "@bazel_tools//platforms:aarch64",
+    ],
+    visibility = ["//visibility:public"],
+)
+
+config_setting(
     name = "linux_x86_64",
     constraint_values = [
         "@bazel_tools//platforms:linux",
@@ -91,6 +100,11 @@
 ) for name in ["make", "jump", "ontop"]]
 
 BOOST_CTX_ASM_SOURCES = select({
+    ":linux_aarch64": [
+        "libs/context/src/asm/jump_arm64_aapcs_elf_gas.S",
+        "libs/context/src/asm/make_arm64_aapcs_elf_gas.S",
+        "libs/context/src/asm/ontop_arm64_aapcs_elf_gas.S",
+    ],
     ":linux_arm": [
         "libs/context/src/asm/jump_arm_aapcs_elf_gas.S",
         "libs/context/src/asm/make_arm_aapcs_elf_gas.S",
@@ -111,6 +125,7 @@
         "libs/context/src/asm/jump_x86_64_ms_pe_masm.S",
         "libs/context/src/asm/ontop_x86_64_ms_pe_masm.S",
     ],
+    "//conditions:default": [],
 })
 
 boost_library(
@@ -125,6 +140,7 @@
         ":windows_x86_64": [
             "libs/context/src/windows/stack_traits.cpp",
         ],
+        "//conditions:default": [],
     }),
     exclude_src = [
         "libs/context/src/fiber.cpp",
@@ -1616,6 +1632,7 @@
             "BOOST_THREAD_USE_LIB",
             "BOOST_WIN32_THREAD",
         ],
+        "//conditions:default": [],
     }),
     linkopts = select({
         ":linux": [