configure: Add check_cpp_condition() helper function to simplify some expressions

configure

@@ -998,6 +998,14 @@ test_cpp_condition(){
 EOF
 }
 
+check_cpp_condition(){
+    log check_cpp_condition "$@"
+    name=$1
+    shift 1
+    disable $name
+    test_cpp_condition "$@" && enable $name
+}
+
 test_cflags_cpp(){
     log test_cflags_cpp "$@"
     flags=$1
@@ -1197,6 +1205,14 @@ test_host_cpp_condition(){
 EOF
 }
 
+check_host_cpp_condition(){
+    log check_host_cpp_condition "$@"
+    name=$1
+    shift 1
+    disable $name
+    test_host_cpp_condition "$@" && enable $name
+}
+
 cp_if_changed(){
     cmp -s "$1" "$2" && { test "$quiet" != "yes" && echo "$2 is unchanged"; } && return
     mkdir -p "$(dirname $2)"
@@ -4232,14 +4248,14 @@ elif enabled alpha; then
 
 elif enabled arm; then
 
-    enabled msvc && test_cpp_condition stddef.h "defined _M_ARMT" && enable thumb
+    enabled msvc && check_cpp_condition thumb stddef.h "defined _M_ARMT"
     test_cpp_condition stddef.h "defined __thumb__" && enable_weak thumb
     enabled thumb && check_cflags -mthumb || check_cflags -marm
 
-    if test_cpp_condition stddef.h "defined __ARM_PCS_VFP"; then
+    if check_cpp_condition vfp_args stddef.h "defined __ARM_PCS_VFP"; then
-        enable vfp_args
+        :
-    elif test_cpp_condition stddef.h "defined _M_ARM_FP && _M_ARM_FP >= 30"; then
+    elif check_cpp_condition vfp_args stddef.h "defined _M_ARM_FP && _M_ARM_FP >= 30"; then
-        enable vfp_args
+        :
     elif ! test_cpp_condition stddef.h "defined __ARM_PCS || defined __SOFTFP__" && [ $target_os != darwin ]; then
         case "${cross_prefix:-$cc}" in
             *hardfloat*)         enable vfp_args;   fpabi=vfp ;;
@@ -4334,7 +4350,7 @@ elif enabled ppc; then
     fi
 
     if enabled power8; then
-        test_cpp_condition "altivec.h" "defined(_ARCH_PWR8)" || disable power8
+        check_cpp_condition power8 altivec.h "defined(_ARCH_PWR8)"
     fi
 
 elif enabled x86; then
@@ -4655,8 +4671,7 @@ enabled libwavpack        && require libwavpack wavpack/wavpack.h WavpackOpenFil
 enabled libwebp           && require_pkg_config libwebp libwebp webp/encode.h WebPGetEncoderVersion
 enabled libx264           && require_pkg_config libx264 x264 "stdint.h x264.h" x264_encoder_encode &&
                              require_cpp_condition x264.h "X264_BUILD >= 118" &&
-                             { test_cpp_condition x264.h "X264_MPEG2" &&
+                             check_cpp_condition libx262 x264.h "X264_MPEG2"
-                               enable libx262; }
 enabled libx265           && require_pkg_config libx265 x265 x265.h x265_api_get &&
                              require_cpp_condition x265.h "X265_BUILD >= 57"
 enabled libxavs           && require libxavs "stdint.h xavs.h" xavs_encoder_encode -lxavs
@@ -4696,7 +4711,7 @@ check_lib user32 "windows.h winuser.h" GetShellWindow -luser32
 check_lib vfw32 "windows.h vfw.h" capCreateCaptureWindow -lvfw32
 # check that WM_CAP_DRIVER_CONNECT is defined to the proper value
 # w32api 3.12 had it defined wrong
-test_cpp_condition vfw.h "WM_CAP_DRIVER_CONNECT > WM_USER" && enable vfwcap_defines
+check_cpp_condition vfwcap_defines vfw.h "WM_CAP_DRIVER_CONNECT > WM_USER"
 
 # check for ioctl_meteor.h, ioctl_bt848.h and alternatives
 check_header "dev/bktr/ioctl_meteor.h dev/bktr/ioctl_bt848.h"                   ||
@@ -4761,8 +4776,7 @@ enabled vaapi &&
     enable vaapi_1
 
 enabled vdpau &&
-    test_cpp_condition vdpau/vdpau.h "defined VDP_DECODER_PROFILE_MPEG4_PART2_ASP" ||
+    check_cpp_condition vdpau vdpau/vdpau.h "defined VDP_DECODER_PROFILE_MPEG4_PART2_ASP"
-    disable vdpau
 
 enabled vdpau &&
     check_lib vdpau_x11 "vdpau/vdpau.h vdpau/vdpau_x11.h" vdp_device_create_x11 -lvdpau -lX11
@@ -4970,7 +4984,7 @@ elif enabled_any msvc icl; then
         disable inline_asm
     fi
     # msvcrt10 x64 incorrectly enables log2, only msvcrt12 (MSVC 2013) onwards actually has log2.
-    test_cpp_condition crtversion.h "_VC_CRT_MAJOR_VERSION >= 12" || disable log2
+    check_cpp_condition log2 crtversion.h "_VC_CRT_MAJOR_VERSION >= 12"
     # The CRT headers contain __declspec(restrict) in a few places, but if redefining
     # restrict, this might break. MSVC 2010 and 2012 fail with __declspec(__restrict)
     # (as it ends up if the restrict redefine is done before including stdlib.h), while