if vs. ifdef in Makefile.am

[ljh]

Hi community,


I want to build debug or release with 


```
$ make # NDEBUG=1
$ make NDEBUG=1
```


Can I have automake.am to define and convey something like this to the output 
Makefile:


```
ifdef NDEBUG             # if vs. ifdef
CPPFLAGS += -DNDEBUG
CFLAGS += -O3 # .cpp
else
CFLAGS += -g # .cpp
LDFLAGS += -fsanitize=address
endif
```


But it seems I can only write `if` but not `ifdef` in Makefile.am.


So I had to enable ndebug option in configure.ac. That's a lot more work.



Thanks