RFR: 8378180: Compiling OpenJDK with C23 C-Compiler gives warning: initialization discards ‘const’ qualifier from pointer target type

[Jasmine Karthikeyan]

Hi all, this is a quick patch to fix a build issue I encountered when updating my Linux system. [Glibc 2.43](https://lists.gnu.org/archive/html/info-gnu/2026-01/msg00005.html) changes the definition of some string related functions to return `const char*` when provided a `const char*` parameter, rather than the previous behavior of returning `char*`. I've fixed this by applying the `const` modifier, and casting to `char*` when needed. This should be backwards-compatible since assigning a non-const pointer to const is an implicit conversion. Thoughts and comments would be appreciated on whether this is the best way to fix this issue. Thanks!

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Commit messages:
 - Fix discarded const qualifiers

Changes: https://git.openjdk.org/jdk/pull/29929/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=29929&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8378180
  Stats: 18 lines in 9 files changed: 0 ins; 0 del; 18 mod
  Patch: https://git.openjdk.org/jdk/pull/29929.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/29929/head:pull/29929

PR: https://git.openjdk.org/jdk/pull/29929