make building SDL app optional, off by default. just build libprojectM by default

configure.ac

@@ -7,18 +7,22 @@ LT_INIT
 AC_PROG_CXX
 
 AC_CONFIG_MACRO_DIRS([m4 m4/autoconf-archive])
-m4_include([m4/sdl2.m4])
 AX_CHECK_GL
 
 AC_CHECK_LIB(c, dlopen, LIBDL="", AC_CHECK_LIB(dl, dlopen, LIBDL="-ldl"))
 
-dnl Check for SDL
-SDL_VERSION=2.0.5
-AS_IF([test "$TRAVIS"], [SDL_VERSION=2.0.2])  # travis has old SDL, we don't care
-AM_PATH_SDL2($SDL_VERSION, :, AC_MSG_WARN([*** SDL version $SDL_VERSION not found!]))
+dnl SDL
+AC_ARG_ENABLE([sdl],
+  AS_HELP_STRING([--enable-sdl], [Build SDL2 app]),
+  [], [enable_sdl=no])
+AS_IF([test "x$enable_sdl" = "xyes"], [
+  m4_include([m4/sdl2.m4])
+  SDL_VERSION=2.0.5
+  AS_IF([test "$TRAVIS"], [SDL_VERSION=2.0.2])  # travis has old SDL, we don't care
+  AM_PATH_SDL2($SDL_VERSION, :, AC_MSG_ERROR([*** SDL version $SDL_VERSION not found!]))
+])
 
 AC_CONFIG_HEADERS([config.h])
-
 AC_CONFIG_FILES([
   Makefile
   src/Makefile
@@ -28,22 +32,14 @@ AC_CONFIG_FILES([
   src/libprojectM/MilkdropPresetFactory/Makefile
   src/projectM-sdl/Makefile
 ])
+dnl FIXME
 AC_CONFIG_FILES([src/libprojectM/config.inp], [sed -i -e"s/\${prefix}/$prefix/" src/libprojectM/config.inp])
 
 AC_PREFIX_DEFAULT([/usr/local])
 
 AC_PROG_MKDIR_P
 
-my_CFLAGS="\
--Wall \
--Wchar-subscripts \
--Wformat-security \
--Wmissing-declarations \
--Wpointer-arith \
--Wshadow \
--Wsign-compare \
--Wtype-limits \
-"
+my_CFLAGS="-Wall -Wchar-subscripts -Wformat-security -Wmissing-declarations -Wpointer-arith -Wshadow -Wsign-compare -Wtype-limits "
 AC_SUBST([my_CFLAGS])
 
 # check OS
@@ -78,4 +74,10 @@ includedir:             ${includedir}
 compiler:               ${CC}
 cflags:                 ${CFLAGS}
 ldflags:                ${LDFLAGS}
+
+
+Applications:
+=====
+
+SDL:                    ${enable_sdl}
 ])