Build a full RocksDB on M1 macs (#7943)

Summary:
With M1 macs being available, it is possible that RocksDB will be built on them, without the resulting artifacts to be intended for iOS, where a non-lite RocksDB is needed.

It is not clear to me why the ROCKSDB_LITE cmake option isn't used for iOS consumer, so sending this pull request as a way to foster discussion and to find a path forward to get a full RocksDB build on M1.

Pull Request resolved: https://github.com/facebook/rocksdb/pull/7943

Test Plan:
Applied the following patch:
```
 diff --git a/fbcode/opensource/fbcode_builder/manifests/rocksdb b/fbcode/opensource/fbcode_builder/manifests/rocksdb
 --- a/fbcode/opensource/fbcode_builder/manifests/rocksdb
+++ b/fbcode/opensource/fbcode_builder/manifests/rocksdb
@@ -2,8 +2,8 @@
 name = rocksdb

 [download]
-url = https://github.com/facebook/rocksdb/archive/v6.8.1.tar.gz
-sha256 = ca192a06ed3bcb9f09060add7e9d0daee1ae7a8705a3d5ecbe41867c5e2796a2
+url = https://github.com/xavierd/rocksdb/archive/master.zip
+sha256 = f93f3f92df66a8401659e35398749d5910b92bd9c14b8354a35ea8852865c422

 [dependencies]
 lz4
@@ -11,7 +11,7 @@

 [build]
 builder = cmake
-subdir = rocksdb-6.8.1
+subdir = rocksdb-master

 [cmake.defines]
 WITH_SNAPPY=ON
```

And ran `getdeps build eden` on an M1 macbook. The build used to fail at link time due to some RocksDB symbols not being found, it now fails for another reason (x86_64 Rust symbols).

Reviewed By: jay-zhuang

Differential Revision: D26324049

Pulled By: xavierd

fbshipit-source-id: 12d86f3395709c4c323f440844e3ae65672aef2d

CMakeLists.txt

@@ -466,11 +466,6 @@ if(CMAKE_SYSTEM_NAME MATCHES "Cygwin")
   add_definitions(-fno-builtin-memcmp -DCYGWIN)
 elseif(CMAKE_SYSTEM_NAME MATCHES "Darwin")
   add_definitions(-DOS_MACOSX)
-  if(CMAKE_SYSTEM_PROCESSOR MATCHES arm)
-    add_definitions(-DIOS_CROSS_COMPILE -DROCKSDB_LITE)
-    # no debug info for IOS, that will make our library big
-    add_definitions(-DNDEBUG)
-  endif()
 elseif(CMAKE_SYSTEM_NAME MATCHES "Linux")
   add_definitions(-DOS_LINUX)
 elseif(CMAKE_SYSTEM_NAME MATCHES "SunOS")