Merge #17880: build: add -Wdate-time to Werror flags

b0a254019c3bc8a353c1304ee65a55cfb3d4ecac build: add Wdate-time to Werror flags (fanquake)

Pull request description:

  `-Wdate-time`
  Warn when macros __TIME__, __DATE__ or __TIMESTAMP__ are encountered as
  they might prevent bit-wise-identical reproducible compilations.

  This is supported by [GCC](https://gcc.gnu.org/onlinedocs/gcc/Warning-Options.html) and [Clang](https://clang.llvm.org/docs/DiagnosticsReference.html#wdate-time).

  Example output:
  ```bash
    CXX      bitcoind-bitcoind.o
  bitcoind.cpp:48:20: warning: expansion of date or time macro is not reproducible [-Wdate-time]
      printf("%s\n", __TIMESTAMP__);
                     ^
  bitcoind.cpp:49:20: warning: expansion of date or time macro is not reproducible [-Wdate-time]
      printf("%s\n", __TIME__);
                     ^
  bitcoind.cpp:50:20: warning: expansion of date or time macro is not reproducible [-Wdate-time]
      printf("%s\n", __DATE__);
                     ^
  3 warnings generated.
  ```

ACKs for top commit:
  practicalswift:
    ACK b0a254019c3bc8a353c1304ee65a55cfb3d4ecac -- diff looks correct and guarding against potential non-reproducibility is good :)
  promag:
    Tested ACK b0a254019c3bc8a353c1304ee65a55cfb3d4ecac on macos with clang. Already had `--enable-werror`, added a wild `printf("%s\n", __TIMESTAMP__)` and got the following error:
  laanwj:
    ACK b0a254019c3bc8a353c1304ee65a55cfb3d4ecac
  hebasto:
    ACK b0a254019c3bc8a353c1304ee65a55cfb3d4ecac

Tree-SHA512: b3a0b426e06dcd0c0baa94118c31158760b9690a8d0a15b5a2d544cb0879522e02817e134ef7346c707de09719818fc7e4bad1b3ad6b2dfe5e3c4169cdf5cb0d

0 files changed, 0 insertions, 0 deletions