RFR: 8311247: Some cpp files are compiled with -std:c11 flag

[Daniel Jeliński]

Please review this patch that configures C++ arguments on build jobs that involve compiling CPP files. As a result of this change, CPP files are compiled with `-std:c++14` command line argument instead of `-std:c11`, which is used when C++ arguments are not configured.
While at it, I simplified the `java.security.jgss/Lib.gmk` file by moving the additional include directory to `EXTRA_HEADER_DIRS`.

This patch fixes the following clang warning:

warning: argument unused during compilation: '-std:c11'


Microsoft states that [std:c++14 is the default](https://learn.microsoft.com/en-us/cpp/build/reference/std-specify-language-standard-version?view=msvc-170), so there shouldn't be any differences in produced code.

Testing:
- verified that after the changes, all CPP files are compiled with `std:c++14` instead of `-std:c11`
- spot-checked a few `cmdline` files that changed after this patch was applied; the `-std` change was the only difference
- tier1-5 builds, tier1-2 tests and client libs tests continue to pass on Windows, Linux & MacOS.

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Commit messages:
 - Update copyright
 - Simplify makefile
 - Revert template changes
 - Use CXXFLAGS where CPP files are compiled

Changes: https://git.openjdk.org/jdk/pull/14758/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=14758&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8311247
  Stats: 22 lines in 5 files changed: 16 ins; 0 del; 6 mod
  Patch: https://git.openjdk.org/jdk/pull/14758.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/14758/head:pull/14758

PR: https://git.openjdk.org/jdk/pull/14758