c4b85ba704a1b5257dc82786a84f676bacb7b027 Bugfix: Define and use HAVE_FDATASYNC correctly outside LevelDB (Luke Dashjr)
Pull request description:
Fixes a bug introduced in #19614
The LevelDB-specific fdatasync check was only using `AC_SUBST`, which works for Makefiles, but doesn't define anything for C++. Furthermore, the #define is typically 0 or 1, never undefined.
This fixes both issues by defining it and checking its value instead of whether it is merely defined.
Pulled out of #14501 by fanquake's request
ACKs for top commit:
fanquake:
ACK c4b85ba704a1b5257dc82786a84f676bacb7b027 - thanks for catching and fixing my mistake.
laanwj:
Code review ACK c4b85ba704a1b5257dc82786a84f676bacb7b027
Tree-SHA512: 91d5d426ba000b4f3ee7e2315635e24bbb23ceff16269ddf4f65a63d25fc9e9cf94a3b236eed2f8031cc36ddcf78aeb5916efcb244f415943a8a12f907ede8f9