configure: move Cocoa incompatibility checks to Meson

The cocoa UI code currently assumes it is always the active UI
and does not interact well with other UI frontend code.  Move
the relevant checks to Meson now that all other frontends
have become Meson options.  This way, SDL/GTK+/Cocoa can be
parsed entirely by scripts/configure-parse-buildoptions.pl.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

configure

@@ -772,7 +772,6 @@ Darwin)
     QEMU_CFLAGS="-arch x86_64 $QEMU_CFLAGS"
     QEMU_LDFLAGS="-arch x86_64 $QEMU_LDFLAGS"
   fi
-  cocoa="enabled"
   audio_drv_list="coreaudio try-sdl"
   audio_possible_drivers="coreaudio sdl"
   QEMU_LDFLAGS="-framework CoreFoundation -framework IOKit $QEMU_LDFLAGS"
@@ -2322,20 +2321,6 @@ if test -z "$want_tools"; then
 fi
 
 ##########################################
-# cocoa implies not SDL or GTK
-# (the cocoa UI code currently assumes it is always the active UI
-# and doesn't interact well with other UI frontend code)
-if test "$cocoa" = "enabled"; then
-    if test "$sdl" = "enabled"; then
-        error_exit "Cocoa and SDL UIs cannot both be enabled at once"
-    fi
-    if test "$gtk" = "enabled"; then
-        error_exit "Cocoa and GTK UIs cannot both be enabled at once"
-    fi
-    gtk=disabled
-    sdl=disabled
-fi
-
 # Some versions of Mac OS X incorrectly define SIZE_MAX
 cat > $TMPC << EOF
 #include <stdint.h>

meson.build

@@ -169,7 +169,6 @@ version_res = []
 coref = []
 iokit = []
 emulator_link_args = []
-cocoa = not_found
 hvf = not_found
 if targetos == 'windows'
   socket = cc.find_library('ws2_32')
@@ -182,7 +181,6 @@ if targetos == 'windows'
 elif targetos == 'darwin'
   coref = dependency('appleframeworks', modules: 'CoreFoundation')
   iokit = dependency('appleframeworks', modules: 'IOKit')
-  cocoa = dependency('appleframeworks', modules: 'Cocoa', required: get_option('cocoa'))
 elif targetos == 'sunos'
   socket = [cc.find_library('socket'),
             cc.find_library('nsl'),
@@ -256,9 +254,6 @@ if not have_xen_pci_passthrough and get_option('xen_pci_passthrough').enabled()
     error('Xen PCI passthrough requested but Xen not enabled')
   endif
 endif
-if not cocoa.found() and get_option('cocoa').enabled()
-  error('Cocoa not available on this platform')
-endif
 
 ################
 # Dependencies #
@@ -362,6 +357,14 @@ if not get_option('attr').disabled()
   endif
 endif
 
+cocoa = dependency('appleframeworks', modules: 'Cocoa', required: get_option('cocoa'))
+if cocoa.found() and get_option('sdl').enabled()
+  error('Cocoa and SDL cannot be enabled at the same time')
+endif
+if cocoa.found() and get_option('gtk').enabled()
+  error('Cocoa and GTK+ cannot be enabled at the same time')
+endif
+
 seccomp = not_found
 if not get_option('seccomp').auto() or have_system or have_tools
   seccomp = dependency('libseccomp', version: '>=2.3.0',
@@ -647,7 +650,7 @@ if not get_option('brlapi').auto() or have_system
 endif
 
 sdl = not_found
-if have_system
+if not get_option('sdl').auto() or (have_system and not cocoa.found())
   sdl = dependency('sdl2', required: get_option('sdl'), static: enable_static)
   sdl_image = not_found
 endif
@@ -779,7 +782,7 @@ endif
 
 gtk = not_found
 gtkx11 = not_found
-if not get_option('gtk').auto() or have_system
+if not get_option('gtk').auto() or (have_system and not cocoa.found())
   gtk = dependency('gtk+-3.0', version: '>=3.22.0',
                    method: 'pkg-config',
                    required: get_option('gtk'),