How to write multiple conditions in Makefile.am with "else if"

I want to compile my project with autoconf/automake. There are 2 conditions defined in my configure.ac

AM_CONDITIONAL(HAVE_CLIENT, test $enable-client -eq 1)
AM_CONDITIONAL(HAVE_SERVER, test $enable-server -eq 1)

I want to separate _LIBS from these 2 conditions in Makefile.am

if HAVE_CLIENT

libtest_LIBS = \

    $(top_builddir)/libclient.la

else if HAVE_SERVER

libtest_LIBS = \

    $(top_builddir)/libserver.la

else

libtest_LIBS = 

endif

but else if HAVE_SERVER does NOT work.

How to write 'else if' in makefile.am?

ptomato's code can also be written in a cleaner manner like:

ifeq ($(TARGET_CPU),x86)
TARGET_CPU_IS_X86 := 1
else ifeq ($(TARGET_CPU),x86_64)
TARGET_CPU_IS_X86 := 1
else
TARGET_CPU_IS_X86 := 0
endif

This doesn't answer OP's question but as it's the top result on google, I'm adding it here in case it's useful to anyone else.

I would accept ldav1s' answer if I were you, but I just want to point out that 'else if' can be written in terms of 'else's and 'if's in any language:

if HAVE_CLIENT
  libtest_LIBS = $(top_builddir)/libclient.la
else
  if HAVE_SERVER
    libtest_LIBS = $(top_builddir)/libserver.la
  else
    libtest_LIBS = 
  endif
endif

(The indentation is for clarity. Don't indent the lines, they won't work.)

ifeq ($(CHIPSET),8960)
   BLD_ENV_BUILD_ID="8960"
else ifeq ($(CHIPSET),8930)
   BLD_ENV_BUILD_ID="8930"
else ifeq ($(CHIPSET),8064)
   BLD_ENV_BUILD_ID="8064"
else ifeq ($(CHIPSET), 9x15)
   BLD_ENV_BUILD_ID="9615"
else
   BLD_ENV_BUILD_ID=
endif

As you've discovered, you can't do that. You can do:

libtest_LIBS = 

...

if HAVE_CLIENT
libtest_LIBS += libclient.la
endif

if HAVE_SERVER
libtest_LIBS += libserver.la
endif

ifdef $(HAVE_CLIENT)
libtest_LIBS = 

$(top_builddir)/libclient.la
else
ifdef $(HAVE_SERVER)
libtest_LIBS = 

$(top_builddir)/libserver.la
else
libtest_LIBS =
endif
endif

NOTE: DO NOT indent the if then it don't work!