Merge #18437: util: Detect posix_fallocate() instead of assuming

182dbdf0f4 util: Detect posix_fallocate() instead of assuming (Vasil Dimov)

Pull request description:

  Don't assume that `posix_fallocate()` is available on Linux and not
  available on other operating systems. At least FreeBSD has it and we
  are not using it.

  Properly check whether `posix_fallocate()` is present and use it if it
  is.

ACKs for top commit:
  laanwj:
    ACK 182dbdf0f4

Tree-SHA512: f9ed4bd661f33ff6b2b1150591e860b3c1f44e12b87c35e870d06a7013c4e841ed2bf17b41ad6b18fe471b0b23a4b5e42cf1400637180888e0bc56c254fe0766

src/util/system.cpp

@@ -17,7 +17,7 @@
 #endif
 
 #ifndef WIN32
-// for posix_fallocate
+// for posix_fallocate, in configure.ac we check if it is present after this
 #ifdef __linux__
 
 #ifdef _POSIX_C_SOURCE
@@ -1019,7 +1019,7 @@ void AllocateFileRange(FILE *file, unsigned int offset, unsigned int length) {
     }
     ftruncate(fileno(file), static_cast<off_t>(offset) + length);
 #else
-    #if defined(__linux__)
+    #if defined(HAVE_POSIX_FALLOCATE)
     // Version using posix_fallocate
     off_t nEndPos = (off_t)offset + length;
     if (0 == posix_fallocate(fileno(file), 0, nEndPos)) return;