Fix the logic of setting read_amp_bytes_per_bit from OPTIONS file (facebook#7680)

Summary:
Instead of using `EncodeFixed32` which always serialize a integer to
little endian, we should use the local machine's endianness when
populating a native data structure during options parsing.
Without this fix, `read_amp_bytes_per_bit` may be populated incorrectly
on big-endian machines.

Pull Request resolved: facebook#7680

Test Plan: make check

Reviewed By: pdillinger

Differential Revision: D24999166

Pulled By: riversand963

fbshipit-source-id: dc603cff6e17f8fa32479ce6df93b93082e6b0c4

Author: riversand963

HISTORY.md

@@ -2,6 +2,7 @@
 ## 6.14.5 (11/15/2020)
 ### Bug Fixes
 * Fix a bug of encoding and parsing BlockBasedTableOptions::read_amp_bytes_per_bit as a 64-bit integer.
+* Fixed the logic of populating native data structure for `read_amp_bytes_per_bit` during OPTIONS file parsing on big-endian architecture. Without this fix, original code introduced in PR7659, when running on big-endian machine, can mistakenly store read_amp_bytes_per_bit (an uint32) in little endian format. Future access to `read_amp_bytes_per_bit` will give wrong values. Little endian architecture is not affected.
 
 ## 6.14.4 (11/05/2020)
 ### Bug Fixes

table/block_based/block_based_table_factory.cc

@@ -347,7 +347,8 @@ static std::unordered_map<std::string, OptionTypeInfo>
             // generated by affected releases before the fix, we need to
             // manually parse read_amp_bytes_per_bit with this special hack.
             uint64_t read_amp_bytes_per_bit = ParseUint64(value);
-            EncodeFixed32(addr, static_cast<uint32_t>(read_amp_bytes_per_bit));
+            *(reinterpret_cast<uint32_t*>(addr)) =
+                static_cast<uint32_t>(read_amp_bytes_per_bit);
             return Status::OK();
           }}},
         {"enable_index_compression",