RFR: JDK-8265373: Change to GCC 10.3 for building on Linux at Oracle [v3]

[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.)

Erik Joelsson has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains seven commits:

 - Merge branch 'master' into gcc-10.3-devkit
 - Fix configure args for linux-x64
 - 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

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Changes: https://git.openjdk.java.net/jdk/pull/3551/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=3551&range=02
  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