Fix build on machines without jemalloc

Summary: It looks like we mistakenly enable JEMALLOC even if it's not available on the machine, that's why travis is failing

Test Plan:
check on my devserver
check on my mac

Reviewers: sdong

Reviewed By: sdong

Subscribers: andrewkr, dhruba

Differential Revision: https://reviews.facebook.net/D57345

build_tools/build_detect_platform

@@ -453,6 +453,6 @@ echo "ROCKSDB_PATCH=$ROCKSDB_PATCH" >> "$OUTPUT"
 echo "CLANG_SCAN_BUILD=$CLANG_SCAN_BUILD" >> "$OUTPUT"
 echo "CLANG_ANALYZER=$CLANG_ANALYZER" >> "$OUTPUT"
 echo "PROFILING_FLAGS=$PROFILING_FLAGS" >> "$OUTPUT"
-if test -z "$JEMALLOC"; then
+if test -n "$JEMALLOC"; then
   echo "JEMALLOC=1" >> "$OUTPUT"
 fi

build_tools/fbcode_config.sh

@@ -61,6 +61,7 @@ CFLAGS+=" -DGFLAGS=google"
 # location of jemalloc
 JEMALLOC_INCLUDE=" -I $JEMALLOC_BASE/include/"
 JEMALLOC_LIB=" $JEMALLOC_BASE/lib/libjemalloc.a"
+JEMALLOC=1
 
 if test -z $PIC_BUILD; then
   # location of numa

build_tools/fbcode_config4.8.1.sh

@@ -40,6 +40,7 @@ GFLAGS_LIBS=" $GFLAGS_BASE/lib/libgflags.a"
 # location of jemalloc
 JEMALLOC_INCLUDE=" -I $JEMALLOC_BASE/include"
 JEMALLOC_LIB="$JEMALLOC_BASE/lib/libjemalloc.a"
+JEMALLOC=1
 
 # location of numa
 NUMA_INCLUDE=" -I $NUMA_BASE/include/"

db/db_impl.cc

@@ -536,6 +536,7 @@ void DBImpl::PrintStatistics() {
   }
 }
 
+#ifndef ROCKSDB_LITE
 #ifdef ROCKSDB_JEMALLOC
 typedef struct {
   char* cur;
@@ -566,6 +567,7 @@ static void DumpMallocStats(std::string* stats) {
   stats->append(buf.get());
 #endif  // ROCKSDB_JEMALLOC
 }
+#endif  // !ROCKSDB_LITE
 
 void DBImpl::MaybeDumpStats() {
   if (db_options_.stats_dump_period_sec == 0) return;