use versions from @bazel_skylib (#81)

Author: oliverlee

version.bzl

@@ -1,5 +1,6 @@
 """Version rules for toolchains"""
 
+load("@bazel_skylib//lib:versions.bzl", compare = "versions")
 load(
     "@toolchains_arm_gnu//toolchain/archives:aarch64_none_elf.bzl",
     "AARCH64_NONE_ELF",
@@ -17,34 +18,12 @@ load(
     "ARM_NONE_LINUX_GNUEABIHF",
 )
 
-def _semver(version):
-    """Parse a semantic version string into a list of integers."""
-    parts = [int(i.split("-")[0]) for i in version.split(".")]
-    return struct(
-        major = parts[0],
-        minor = parts[1],
-        patch = parts[2],
-    )
-
-def _compare_versions(left, right):
-    """Compare two semantic versions."""
-    left = _semver(left)
-    right = _semver(right)
-
-    # (a < b): -1, (a > b): 1, (a == b): 0.
-    compare = lambda a, b: int(a > b) - int(a < b)
-
-    return compare(left.major, right.major) or \
-           compare(left.minor, right.minor) or \
-           compare(left.patch, right.patch) or \
-           0
-
 def max_version(versions):
     """Obtains the minimum version from the list of version strings."""
     if versions:
         maximum = versions.pop(0)
         for version in versions:
-            if _compare_versions(maximum, version) < 0:
+            if not compare.is_at_most(maximum, version):
                 maximum = version
         return maximum
     return None
@@ -54,7 +33,7 @@ def min_version(versions):
     if versions:
         minimum = versions.pop(0)
         for version in versions:
-            if _compare_versions(minimum, version) > 0:
+            if not compare.is_at_least(minimum, version):
                 minimum = version
         return minimum
     return None