Update versions of archives in WORKSPACE (#775)

The m4/flex/bison commits are in, unreleased, but we can still go back to the canonical repo. Also updates the python version.

This pulls out the version statement mainly because it's typically repeated, not due to the m4/flex/bison verbosity. Pulling it out makes it more obvious and easier to change.

WORKSPACE

@@ -6,11 +6,16 @@ workspace(name = "carbon")
 
 load("@bazel_tools//tools/build_defs/repo:http.bzl", "http_archive")
 
+rules_python_version = "0.3.0"
+
 # Add Bazel's python rules and set up pip.
 http_archive(
     name = "rules_python",
-    sha256 = "b6d46438523a3ec0f3cead544190ee13223a52f6a6765a29eae7b7cc24cc83a0",
-    url = "https://github.com/bazelbuild/rules_python/releases/download/0.1.0/rules_python-0.1.0.tar.gz",
+    sha256 = "934c9ceb552e84577b0faf1e5a2f0450314985b4d8712b2b70717dc679fdc01b",
+    url = "https://github.com/bazelbuild/rules_python/releases/download/%s/rules_python-%s.tar.gz" % (
+        rules_python_version,
+        rules_python_version,
+    ),
 )
 
 load("@rules_python//python:pip.bzl", "pip_install")
@@ -22,7 +27,10 @@ pip_install(
 )
 
 # Configure the bootstrapped Clang and LLVM toolchain for Bazel.
-load("//bazel/cc_toolchains:clang_configuration.bzl", "configure_clang_toolchain")
+load(
+    "//bazel/cc_toolchains:clang_configuration.bzl",
+    "configure_clang_toolchain",
+)
 
 configure_clang_toolchain(name = "bazel_cc_toolchain")
 
@@ -53,16 +61,16 @@ load("@llvm_bazel//:zlib.bzl", "llvm_zlib_system")
 # We require successful detection and use of a system zlib library.
 llvm_zlib_system(name = "llvm_zlib")
 
-# TODO(chandlerc): Replace this with an upstream release once the pull request
-# with our needed functionality lands:
-# https://github.com/jmillikin/rules_m4/pull/7
-#
-# Until then, this is pulling from that pull request's commit.
+# TODO: Can switch to a normal release version when it includes:
+# https://github.com/jmillikin/rules_m4/commit/b504241407916d1d6d72c66a766daacf9603cf8b
+rules_m4_version = "b504241407916d1d6d72c66a766daacf9603cf8b"
+
 http_archive(
     name = "rules_m4",
-    sha256 = "4d34917214e8890ad770bdf0c319c41c9201fffd770938b41a1d641d4b27e05c",
-    strip_prefix = "rules_m4-add-extra-copts",
-    urls = ["https://github.com/chandlerc/rules_m4/archive/add-extra-copts.zip"],
+    sha256 = "e6003c5f45746a2ad01335a8526044591f2b6c5c68852cee1bcd28adc2cf452b",
+    strip_prefix = "rules_m4-%s" % rules_m4_version,
+    urls = ["https://github.com/jmillikin/rules_m4/archive/%s.zip" %
+            rules_m4_version],
 )
 
 load("@rules_m4//m4:m4.bzl", "m4_register_toolchains")
@@ -71,16 +79,16 @@ load("@rules_m4//m4:m4.bzl", "m4_register_toolchains")
 # them anyways.
 m4_register_toolchains(extra_copts = ["-w"])
 
-# TODO(chandlerc): Replace this with an upstream release once the pull request
-# with our needed functionality lands:
-# https://github.com/jmillikin/rules_flex/pull/5
-#
-# Until then, this is pulling from that pull request's commit.
+# TODO: Can switch to a normal release version when it includes:
+# https://github.com/jmillikin/rules_flex/commit/1f1d9c306c2b4b8be2cb899a3364b84302124e77
+rules_flex_version = "1f1d9c306c2b4b8be2cb899a3364b84302124e77"
+
 http_archive(
     name = "rules_flex",
-    sha256 = "fd97c3ae23926507be1b95158a683cd41c628d201e852a325d38b5e9f821b752",
-    strip_prefix = "rules_flex-add-extra-copts",
-    urls = ["https://github.com/chandlerc/rules_flex/archive/add-extra-copts.zip"],
+    sha256 = "ad1c3a1a9bdd6254df857f84f3ab4c052df6e21ce4af5d32710f2feff2abf4dd",
+    strip_prefix = "rules_flex-%s" % rules_flex_version,
+    urls = ["https://github.com/jmillikin/rules_flex/archive/%s.zip" %
+            rules_flex_version],
 )
 
 load("@rules_flex//flex:flex.bzl", "flex_register_toolchains")
@@ -89,16 +97,16 @@ load("@rules_flex//flex:flex.bzl", "flex_register_toolchains")
 # fix them anyways.
 flex_register_toolchains(extra_copts = ["-w"])
 
-# TODO(chandlerc): Replace this with an upstream release once the pull request
-# with our needed functionality lands:
-# https://github.com/jmillikin/rules_bison/pull/7
-#
-# Until then, this is pulling from that pull request's commit.
+# TODO: Can switch to a normal release version when it includes:
+# https://github.com/jmillikin/rules_bison/commit/478079b28605a38000eaf83719568d756b3383a0
+rules_bison_version = "478079b28605a38000eaf83719568d756b3383a0"
+
 http_archive(
     name = "rules_bison",
-    sha256 = "c6e926f15214d903966dc950d759ec69116db67f148be114c119e4def0551eaa",
-    strip_prefix = "rules_bison-add-extra-copts",
-    urls = ["https://github.com/chandlerc/rules_bison/archive/add-extra-copts.zip"],
+    sha256 = "d662d200f4e2a868f6873d666402fa4d413f07ba1a433591c5f60ac601157fb9",
+    strip_prefix = "rules_bison-%s" % rules_bison_version,
+    urls = ["https://github.com/jmillikin/rules_bison/archive/%s.zip" %
+            rules_bison_version],
 )
 
 load("@rules_bison//bison:bison.bzl", "bison_register_toolchains")