Fix compile error with aligned-new (#4576)

Summary:
In fbcode when we build with clang7++, although -faligned-new is available in compile phase, we link with an older version of libstdc++.a and it doesn't come with aligned-new support (e.g. `nm libstdc++.a | grep align_val_t` return empty). In this case the previous -faligned-new detection can pass but will end up with link error. Fixing it by only have the detection for non-fbcode build.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/4576

Differential Revision: D10500008

Pulled By: yiwu-arbug

fbshipit-source-id: b375de4fbb61d2a08e54ab709441aa8e7b4b08cf

Makefile

@@ -102,10 +102,6 @@ OPT += -momit-leaf-frame-pointer
 endif
 endif
 
-ifeq (,$(shell $(CXX) -fsyntax-only -faligned-new -xc++ /dev/null 2>&1))
-CXXFLAGS += -faligned-new -DHAVE_ALIGNED_NEW
-endif
-
 ifeq (,$(shell $(CXX) -fsyntax-only -maltivec -xc /dev/null 2>&1))
 CXXFLAGS += -DHAS_ALTIVEC
 CFLAGS += -DHAS_ALTIVEC

build_tools/build_detect_platform

@@ -474,6 +474,17 @@ EOF
             COMMON_FLAGS="$COMMON_FLAGS -DROCKSDB_SCHED_GETCPU_PRESENT"
         fi
     fi
+
+    if ! test $ROCKSDB_DISABLE_ALIGNED_NEW; then
+        # Test whether c++17 aligned-new is supported
+        $CXX $PLATFORM_CXXFLAGS -faligned-new -x c++ - -o /dev/null 2>/dev/null <<EOF
+            struct alignas(1024) t {int a;};
+            int main() {}
+EOF
+        if [ "$?" = 0 ]; then
+            PLATFORM_CXXFLAGS="$PLATFORM_CXXFLAGS -faligned-new -DHAVE_ALIGNED_NEW"
+        fi
+    fi
 fi
 
 # TODO(tec): Fix -Wshorten-64-to-32 errors on FreeBSD and enable the warning.