Issue #, if available:
#3613

Description of changes:
This PR adds an opt-out CMake option to prevent the AWS SDK for C++ from exporting
the C++ language standard via pkg-config Cflags.

Currently, the generated .pc files include compiler policy flags (e.g.
-std=c++<N>, -fno-exceptions) derived from AWS_COMPILER_FLAGS. Downstream
projects that consume the SDK using pkg-config (for example, Meson or custom
build systems) blindly apply these flags, which can override the consumer’s
chosen C++ standard and cause build failures.

To address this without breaking existing users, this PR introduces a new option:

-DNO_CPPSTD_IN_PKG_CONFIG=ON

When enabled, the generated pkg-config Cflags will no longer include:

• -std=c++<N> (primary issue reported)
• -fno-exceptions (also identified as leaking semantics into downstream builds)

The default behavior remains unchanged to preserve backward compatibility.
CMake-based consumers are unaffected, as these flags remain PRIVATE to SDK
targets.

Check all that applies:

• Did a review by yourself.

• Added proper tests to cover this PR.
  Two Docker-based tests were used:
  - One Dockerfile builds the upstream SDK and a minimal downstream project
  to reliably reproduce the reported failure. Docker_Issue_Repro.zip
  - A second Dockerfile builds the SDK with this patch enabled and verifies
  that the downstream project builds successfully.Docker-Fix-Verify.zip

• Checked if this PR is a breaking (APIs have been changed) change.

• Checked if this PR will not introduce cross-platform inconsistent behavior.

• Checked if this PR would require a ReadMe/Wiki update.

Check which platforms you have built SDK on to verify the correctness of this PR.

• Linux
• Windows
• Android
• MacOS
• IOS
• Other Platforms

Screenshots:

Issue Reproduced:

Fix-Verify:

By submitting this pull request, I confirm that you can use, modify, copy, and
redistribute this contribution, under the terms of your choice.

Sign-off: Rajan Y.(rajanyadav0307@gmail.com)