RFR: 8308290: Add fontconfig requirement to building.md

[Jan Kratochvil]

After following all the commands in `building.md` I still get on Fedora 38 x86_64:


checking for fontconfig/fontconfig.h... no
configure: error: Could not find fontconfig!


Another issue is that it is all written with `yum` instead of `dnf` but people can handle it I guess.

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Commit messages:
 - 8308290: Add fontconfig requirement to building.md

Changes: https://git.openjdk.org/jdk/pull/14034/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=14034&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8308290
  Stats: 23 lines in 2 files changed: 23 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/14034.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/14034/head:pull/14034

PR: https://git.openjdk.org/jdk/pull/14034