RFR: 8323700: Add fontconfig requirement to building.md for Alpine Linux [v2]

[Jan Kratochvil]

> Similar to JDK-8309287.

Jan Kratochvil has updated the pull request incrementally with one additional commit since the last revision:

  Update doc/building.html

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Changes:
  - all: https://git.openjdk.org/jdk/pull/17415/files
  - new: https://git.openjdk.org/jdk/pull/17415/files/2a4247a5..913b91d2

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=17415&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=17415&range=00-01

  Stats: 2 lines in 1 file changed: 2 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/17415.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/17415/head:pull/17415

PR: https://git.openjdk.org/jdk/pull/17415