Fix format_compatible blowing away its TEST_TMPDIR (#9970)

Summary:
https://github.com/facebook/rocksdb/issues/9961 broke format_compatible check because of `make clean`
referencing TEST_TMPDIR. The Makefile behavior seems reasonable to me,
so here's a fix in check_format_compatible.sh

Apparently I also included removing a redundant part of our CircleCI config.

Pull Request resolved: https://github.com/facebook/rocksdb/pull/9970

Test Plan: manual run: SHORT_TEST=1 ./tools/check_format_compatible.sh

Reviewed By: riversand963

Differential Revision: D36258172

Pulled By: pdillinger

fbshipit-source-id: d46507f04614e888b414ff23b88d040ae2b5c294

.circleci/config.yml

@@ -417,7 +417,7 @@ jobs:
     steps:
       - checkout # check out the code in the project directory
       - run: apt-get update -y && apt-get install -y libgflags-dev
-      - run: TEST_TMPDIR=/dev/shm && make V=1 -j8 unity_test
+      - run: make V=1 -j8 unity_test
       - run: make V=1 -j8 -k check-headers # could be moved to a different build
       - post-steps
 

tools/check_format_compatible.sh

@@ -63,6 +63,9 @@ scriptpath=`dirname ${BASH_SOURCE[0]}`
 test_dir=${TEST_TMPDIR:-"/tmp"}"/rocksdb_format_compatible_$USER"
 rm -rf ${test_dir:?}
 
+# Prevent 'make clean' etc. from wiping out test_dir
+export TEST_TMPDIR=$test_dir"/misc"
+
 # For saving current version of scripts as we checkout different versions to test
 script_copy_dir=$test_dir"/script_copy"
 mkdir -p $script_copy_dir