Allow user to pass git command to makefile (#10318)

Summary:
This allows users to pass their git command with extra options if necessary.

Pull Request resolved: https://github.com/facebook/rocksdb/pull/10318

Reviewed By: ajkr

Differential Revision: D37661175

Pulled By: lth

fbshipit-source-id: 2a7cf27626c74f167471e6ec57e3870630a582b0

Makefile

@@ -136,6 +136,7 @@ CXXFLAGS += $(PLATFORM_SHARED_CFLAGS) -DROCKSDB_DLL
 CFLAGS +=  $(PLATFORM_SHARED_CFLAGS) -DROCKSDB_DLL
 endif
 
+GIT_COMMAND ?= git
 ifeq ($(USE_COROUTINES), 1)
 	USE_FOLLY = 1
 	OPT += -DUSE_COROUTINES
@@ -2356,9 +2357,9 @@ commit_prereq:
 # integration.
 checkout_folly:
 	if [ -e third-party/folly ]; then \
-		cd third-party/folly && git fetch origin; \
+		cd third-party/folly && ${GIT_COMMAND} fetch origin; \
 	else \
-		cd third-party && git clone https://github.com/facebook/folly.git; \
+		cd third-party && ${GIT_COMMAND} clone https://github.com/facebook/folly.git; \
 	fi
 	@# Pin to a particular version for public CI, so that PR authors don't
 	@# need to worry about folly breaking our integration. Update periodically