fix: cannot build 'gerrit-3.2' on MacOS

When `bazel build release` is called the following issue is being
thrown:
  ERROR: /Users/jacek.centkowski/workspace/open/open-source/gerrit/plugins/gitiles/BUILD:23:9: Executing genrule //plugins/gitiles:gitiles-servlet-resources failed: (Exit 1): bash failed: error executing command /bin/bash -c ... (remaining 1 argument(s) skipped)

  Use --sandbox_debug to see verbose messages from the sandbox
  sed: -I or -i may not be used with stdin
  Target //plugins/gitiles:gitiles failed to build

It seems that 'Load fonts directly from Gerrit instead of 3rd party
domains' introduced the `sed` transformation that is not supported under
MacOS. As suggested in [1] the most portable way is to handle the backup
file in the command line (at least it works on MacOS ;)).

[1] https://stackoverflow.com/a/21243111

Bug: Issue 15307
Change-Id: I3c40bc42d0a0d1a25aacd1cd2687af03970f88b4

BUILD

diff --git a/BUILD b/BUILD
index 6aa6df5..057d3d2 100644
--- a/BUILD
+++ b/BUILD
@@ -29,13 +29,17 @@
         "cd $$TMP/com/google/gitiles/static",
         # To avoid loading 3rd party resources, we adapt gitiles' CSS to
         # load fonts from Gerrit directly:
-        # 1. Strip out Google font CSS imports
-        "sed -e '\\%^@import .//fonts\\.googleapis\\.com/%d' -i base.css",
+        # 1. Strip out Google font CSS imports to tmp file as in-place replace is OSX no-go
+        "sed -e '\\%^@import .//fonts\\.googleapis\\.com/%d' base.css > $$TMP/base.css.tmp",
+        # move tmp file back to base.css
+        "mv $$TMP/base.css.tmp base.css",
         # 2. Add Gerrit's fonts CSS
         "sed -e 's%^\\(.*Common styles and definitions.*\\)$$%" +
-          "\\1\\n\\n@import \"../../../styles/fonts.css\";%' -i base.css",
+          "\\1\\n\\n@import \"../../../styles/fonts.css\";%' base.css > $$TMP/base.css.tmp",
+        "mv $$TMP/base.css.tmp base.css",
         # 3. Use Gerrit's Roboto Mono for Source Code Pro
-        "sed -e 's/Source Code Pro/Roboto Mono/g' -i base.css",
+        "sed -e 's/Source Code Pro/Roboto Mono/g' base.css > $$TMP/base.css.tmp",
+        "mv $$TMP/base.css.tmp base.css",
         # Switching from `static` to `+static` (see comment in plugin definiton)
         "cd $$TMP/com/google/gitiles",
         "mv static +static",