Use fallocate even if hole-punching unsupported (facebook#5023)

Summary:
The compiler flag `-DROCKSDB_FALLOCATE_PRESENT` was only set when
`fallocate`, `FALLOC_FL_KEEP_SIZE`, and `FALLOC_FL_PUNCH_HOLE` were all
present. However, the last of the three is not really necessary for the
primary `fallocate` use case; furthermore, it was introduced only in later
Linux kernel versions (2.6.38+).

This PR changes the flag `-DROCKSDB_FALLOCATE_PRESENT` to only require
`fallocate` and `FALLOC_FL_KEEP_SIZE` to be present. There is a separate
check for `FALLOC_FL_PUNCH_HOLE` only in the place where it is used.
Pull Request resolved: facebook#5023

Differential Revision: D14248487

Pulled By: siying

fbshipit-source-id: a10ed0b902fa755988e957bd2dcec9081ec0502e

CMakeLists.txt

@@ -416,7 +416,7 @@ if(WITH_FALLOCATE)
 #include <linux/falloc.h>
 int main() {
  int fd = open(\"/dev/null\", 0);
- fallocate(fd, FALLOC_FL_KEEP_SIZE | FALLOC_FL_PUNCH_HOLE, 0, 1024);
+ fallocate(fd, FALLOC_FL_KEEP_SIZE, 0, 1024);
 }
 " HAVE_FALLOCATE)
   if(HAVE_FALLOCATE)

build_tools/build_detect_platform

@@ -234,7 +234,7 @@ else
           #include <linux/falloc.h>
           int main() {
       int fd = open("/dev/null", 0);
-      fallocate(fd, FALLOC_FL_KEEP_SIZE | FALLOC_FL_PUNCH_HOLE, 0, 1024);
+      fallocate(fd, FALLOC_FL_KEEP_SIZE, 0, 1024);
           }
 EOF
         if [ "$?" = 0 ]; then

env/io_posix.cc

@@ -825,7 +825,8 @@ Status PosixWritableFile::Close() {
     // but it will be nice to log these errors.
     int dummy __attribute__((__unused__));
     dummy = ftruncate(fd_, filesize_);
-#if defined(ROCKSDB_FALLOCATE_PRESENT) && !defined(TRAVIS)
+#if defined(ROCKSDB_FALLOCATE_PRESENT) && defined(FALLOC_FL_PUNCH_HOLE) && \
+        !defined(TRAVIS)
     // in some file systems, ftruncate only trims trailing space if the
     // new file size is smaller than the current size. Calling fallocate
     // with FALLOC_FL_PUNCH_HOLE flag to explicitly release these unused