[jdk11u-dev] RFR: 8265531: doc/building.md should mention homebrew install freetype

[George Adams]

simple backport of https://bugs.openjdk.org/browse/JDK-8265531 - no risk

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Commit messages:
 - Backport 5aab1609b97284ccff8b7ae20a3ddcf1e29c47d7

Changes: https://git.openjdk.org/jdk11u-dev/pull/1236/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk11u-dev&pr=1236&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8265531
  Stats: 2 lines in 2 files changed: 2 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk11u-dev/pull/1236.diff
  Fetch: git fetch https://git.openjdk.org/jdk11u-dev pull/1236/head:pull/1236

PR: https://git.openjdk.org/jdk11u-dev/pull/1236