I want to compile my project with autoconf/automake. There are 2 conditions defined in my configure.ac
AM_CONDITIONAL(HAVE_CLIENT, test $enable-client -eq 1)
AM_         
        ifeq ($(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 ($(CHIPSET), 9x15)
   BLD_ENV_BUILD_ID="9615"
else
   BLD_ENV_BUILD_ID=
endif
ptomato's code can also be written in a cleaner manner like:
ifeq ($(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.
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
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.)
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!