Fix gflags Makefile

Summary: `echo` correctly interpretes \n on mac, but not on linux. On linux you have to give it `-e` to interpret \n. Unfortunately, `-e` options is not available on Mac. Go back to old way of checking gflags

Test Plan: build_tools/build_detect_platform on mac and linux

Reviewers: sdong

Subscribers: dhruba

Differential Revision: https://reviews.facebook.net/D37515

build_tools/build_detect_platform

@@ -203,13 +203,22 @@ EOF
     # Test whether gflags library is installed
     # http://code.google.com/p/gflags/
     # check if the namespace is gflags
-    if echo "#include <gflags/gflags.h>\nusing namespace gflags;\nint main() {}" | \
-      $CXX $CFLAGS -x c++ - -o /dev/null 2>/dev/null; then
+    $CXX $CFLAGS -x c++ - -o /dev/null 2>/dev/null << EOF
+      #include <gflags/gflags.h>
+      using namespace gflags;
+      int main() {}
+EOF
+    if [ "$?" = 0 ]; then
         COMMON_FLAGS="$COMMON_FLAGS -DGFLAGS=gflags"
         PLATFORM_LDFLAGS="$PLATFORM_LDFLAGS -lgflags"
     else
-      if echo "#include <gflags/gflags.h>\nusing namespace google;\nint main() {}" | \
-        $CXX $CFLAGS -x c++ - -o /dev/null 2> /dev/null; then
+      # check if namespace is google
+      $CXX $CFLAGS -x c++ - -o /dev/null 2>/dev/null << EOF
+        #include <gflags/gflags.h>
+        using namespace google;
+        int main() {}
+EOF
+      if [ "$?" = 0 ]; then
           COMMON_FLAGS="$COMMON_FLAGS -DGFLAGS=google"
           PLATFORM_LDFLAGS="$PLATFORM_LDFLAGS -lgflags"
       fi