add pthreadpool

.gitmodules

@@ -10,3 +10,6 @@
 [submodule "third-party/gflags"]
 	path = third-party/gflags
 	url = https://github.com/gflags/gflags.git
+[submodule "backends/xnnpack/third-party/pthreadpool"]
+	path = backends/xnnpack/third-party/pthreadpool
+	url = https://github.com/Maratyszcza/pthreadpool.git

backends/xnnpack/third-party/TARGETS

@@ -0,0 +1,3 @@
+load(":pthreadpool_defs.bzl", "define_pthreadpool")
+
+define_pthreadpool()

backends/xnnpack/third-party/pthreadpool_defs.bzl

@@ -0,0 +1,39 @@
+def define_pthreadpool():
+    # @lint-ignore BUCKLINT: native and fb_native are explicitly forbidden in fbcode.
+    native.cxx_library(
+        name = "pthreadpool",
+        srcs = ["pthreadpool/src/legacy-api.c", "pthreadpool/src/memory.c", "pthreadpool/src/portable-api.c", "pthreadpool/src/pthreads.c"],
+        deps = [
+            ":FXdiv",
+        ],
+        exported_deps = [
+            ":pthreadpool_header",
+        ],
+        compiler_flags = [
+            "-w",
+            "-Os",
+            "-fstack-protector-strong",
+            "-fno-delete-null-pointer-checks",
+        ],
+        headers = {
+            "threadpool-atomics.h": "pthreadpool/src/threadpool-atomics.h",
+            "threadpool-common.h": "pthreadpool/src/threadpool-common.h",
+            "threadpool-object.h": "pthreadpool/src/threadpool-object.h",
+            "threadpool-utils.h": "pthreadpool/src/threadpool-utils.h",
+        },
+        header_namespace = "",
+        preferred_linkage = "static",
+        platform_preprocessor_flags = [["windows", ["-D_WINDOWS", "-D_WIN32", "-DWIN32", "-DNOMINMAX", "-D_CRT_SECURE_NO_WARNINGS", "-D_USE_MATH_DEFINES"]], ["windows.*64$", ["-D_WIN64"]]],
+        preprocessor_flags = ["-DPTHREADPOOL_USE_FUTEX=0", "-DPTHREADPOOL_USE_GCD=0"],
+        visibility = ["PUBLIC"],
+    )
+
+    # @lint-ignore BUCKLINT: native and fb_native are explicitly forbidden in fbcode.
+    native.cxx_library(
+        name = "pthreadpool_header",
+        header_namespace = "",
+        exported_headers = {
+            "pthreadpool.h": "pthreadpool/include/pthreadpool.h",
+        },
+        visibility = ["PUBLIC"],
+    )