Add more GCC flags to CI builds

[marvinborner]

Within the last few weeks we've repeatedly had compilation warnings in the LLVM backend compiled with the master branch. The warnings could have been caught earlier by running Effekt with the --debug flag.

To enforce this, the CI now runs with --debug by default (in addition to --valgrind) and --debug adds the additional -Werror flag -- thus failing the CI if the compilation produces warnings.

[b-studios]

Using these --debug flags on my machine result in the following now errors

In file included from /User/../../llvm/main.c:14:
/User/../../llvm/bytearray.c:84:5: error: 'sprintf' is deprecated: This function is provided for compatibility reasons only.  Due to security concerns inherent in the design of sprintf(3), it is highly recommended that you use snprintf(3) instead. [-Werror,-Wdeprecated-declarations]
   84 |     sprintf(str, "%" PRId64, n);
      |     ^
/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/_stdio.h:274:1: note: 'sprintf' has been explicitly marked deprecated here
  274 | __deprecated_msg("This function is provided for compatibility reasons only.  Due to security concerns inherent in the design of sprintf(3), it is highly recommended that you use snprintf(3) instead.")
      | ^
/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/sys/cdefs.h:218:48: note: expanded from macro '__deprecated_msg'
  218 |         #define __deprecated_msg(_msg) __attribute__((__deprecated__(_msg)))
      |                                                       ^
In file included from /User/../../llvm/main.c:14:
/User/../../llvm/bytearray.c:115:5: error: 'sprintf' is deprecated: This function is provided for compatibility reasons only.  Due to security concerns inherent in the design of sprintf(3), it is highly recommended that you use snprintf(3) instead. [-Werror,-Wdeprecated-declarations]
  115 |     sprintf(str, "%" PRIu8, n);
      |     ^
/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/_stdio.h:274:1: note: 'sprintf' has been explicitly marked deprecated here
  274 | __deprecated_msg("This function is provided for compatibility reasons only.  Due to security concerns inherent in the design of sprintf(3), it is highly recommended that you use snprintf(3) instead.")
      | ^
/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/sys/cdefs.h:218:48: note: expanded from macro '__deprecated_msg'
  218 |         #define __deprecated_msg(_msg) __attribute__((__deprecated__(_msg)))
      |                                                       ^
In file included from /User/../../llvm/main.c:14:
/User/../../llvm/bytearray.c:122:5: error: 'sprintf' is deprecated: This function is provided for compatibility reasons only.  Due to security concerns inherent in the design of sprintf(3), it is highly recommended that you use snprintf(3) instead. [-Werror,-Wdeprecated-declarations]
  122 |     sprintf(str, "%g", x);
      |     ^
/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/_stdio.h:274:1: note: 'sprintf' has been explicitly marked deprecated here
  274 | __deprecated_msg("This function is provided for compatibility reasons only.  Due to security concerns inherent in the design of sprintf(3), it is highly recommended that you use snprintf(3) instead.")
      | ^
/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/sys/cdefs.h:218:48: note: expanded from macro '__deprecated_msg'
  218 |         #define __deprecated_msg(_msg) __attribute__((__deprecated__(_msg)))
      |                                                       ^