RFR: JDK-8265373: Change to GCC 10.3 for building on Linux at Oracle

[Erik Joelsson]

Oracle is updating the version of GCC for building the JDK to 10.3.

In addition to the version bump, I'm also enabling cross compilation OOTB using jib from a linux-aarch64 to linux-x64 binaries, which was the last missing combination. (Native x64, native aarch64, cross from x64 to aarch64 all worked already and will continue to do so.)

-------------

Commit messages:
 - Finalize devkits
 - Merge branch 'master' into gcc-10.3-devkit
 - Corrected condition for --build-devkit
 - Enable cross building from aarch64 to x64
 - Use GCC 10.3 by default for devkit creation

Changes: https://git.openjdk.java.net/jdk/pull/3551/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=3551&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8265373
  Stats: 27 lines in 2 files changed: 14 ins; 4 del; 9 mod
  Patch: https://git.openjdk.java.net/jdk/pull/3551.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/3551/head:pull/3551

PR: https://git.openjdk.java.net/jdk/pull/3551