fix: Pass Velox CMake build type to Folly

[yingsu00]

Currently Velox never passes CMAKE_BUILD_TYPE into Folly's own configure step, while cmake_install only forwards arbitrary caller flags, so Folly was not built in release mode when Velox is built in release mode. This commit adds -DCMAKE_BUILD_TYPE="${CMAKE_BUILD_TYPE}" to FOLLY_FLAGS, so a release Velox dependency setup now builds release Folly on macOS and Linux.

The TPCH 1TB shows

• 8% wall time improvement for the whole run (1 cold 1 warm)
• 12.7% wall time improvement for warm run
• PartitionedOutput shows 19% improvement in CPU time

The improvements is presumably from the Folly hash function speed up in release build.

Detailed comparisons can be found here

Whole run 1cold 1 warm elapsed
713,081 vs. 659,360.  8% improvement

Warm only
285,687 vs. 253,468. 12.7% improvement

PartitionedOutput  CPU
6,978,244 vs. 5,852,930  19% improvement

[xin-zhang2]

@yingsu00 Thanks! Should this change also be delivered into the upstream velox?

[yingsu00]

@yingsu00 Thanks! Should this change also be delivered into the upstream velox?

Not really. We want to use upstream Velox as a baseline so I won't send PRs to FB upstream.