Rename system_error to system_error_t

[sergeuz]

Problem

C++11 defines std::system_error class which may cause global name conflicts with the firmware's system_error enum, especially in applications that abuse using namespace std.

Solution

Rename system_error enum to system_error_t. We never exposed system_error as part of any public API, so the fix won't affect existing applications.

Steps to Test

The firmware and unit tests should build normally.

Example App

N/A

References

Original community post: https://community.particle.io/t/compile-error-gcc-arm-on-linux-firmware-v-0-6-1/31157

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Completeness

• User is totes amazing for contributing!
• Contributor has signed CLA (Info here)
• Problem and Solution clearly stated
• Run unit/integration/application tests on device
• Added documentation
• Added to CHANGELOG.md after merging (add links to docs and issues)

Bugfix

• [PR #1326] Renamed system_error enum to system_error_t to avoid conflicts with std::system_error class.