Convert the compression level to a string before calling Args.add() (#975)

The documentation for Bazel's Args states that standard conversion rules
are only specified for strings, Files, and Labels. For all other types
the conversion to a string is done in an unspecified manner, which is
why it should be avoided.

Let's stay away from this unspecified behaviour by explicitly converting
the compression level to a string before calling Args.add().

pkg/private/tar/tar.bzl

diff --git a/pkg/private/tar/tar.bzl b/pkg/private/tar/tar.bzl
index 1d4755a..75876b8 100644
--- a/pkg/private/tar/tar.bzl
+++ b/pkg/private/tar/tar.bzl
@@ -115,7 +115,7 @@
                 "%s=%s" % (_quote(key), ctx.attr.ownernames[key]),
             )
     if ctx.attr.compression_level:
-        args.add("--compression_level", ctx.attr.compression_level)
+        args.add("--compression_level", str(ctx.attr.compression_level))
 
     # Now we begin processing the files.
     path_mapper = None

toolchains/rpm/rpmbuild_configure.bzl

diff --git a/toolchains/rpm/rpmbuild_configure.bzl b/toolchains/rpm/rpmbuild_configure.bzl
index 6ae3674..2f3c7e5 100644
--- a/toolchains/rpm/rpmbuild_configure.bzl
+++ b/toolchains/rpm/rpmbuild_configure.bzl
@@ -82,7 +82,7 @@
         fail("debuginfo_type must be one of", DEBUGINFO_VALID_VALUES)
 
     debuginfo_type = rctx.attr.debuginfo_type
-    if debuginfo_type == DEBUGINFO_TYPE_AUTODETECT:   
+    if debuginfo_type == DEBUGINFO_TYPE_AUTODETECT:
         if rctx.path(RELEASE_PATH).exists:
             rctx.watch(RELEASE_PATH)
             os_name, _ = _parse_release_info(rctx.read(RELEASE_PATH))