fix Android standalone toolchain build

add a check for cpu-features.h and rework some of the ifdef's around
android + neon. for android builds with cpu-features enabled the
*_neon.c files will still need to be flagged correctly (with e.g.,
.c.neon in Android.mk) to properly build them.

BUG=webp:353

Change-Id: I905ce305af0a204e560b915d8665093a3edaceb9
(cherry picked from commit c6d1db4b36)

Android.mk

@@ -25,6 +25,7 @@ ifneq ($(findstring armeabi-v7a, $(TARGET_ARCH_ABI)),)
   # specifically.
   NEON := c.neon
   USE_CPUFEATURES := yes
+  WEBP_CFLAGS += -DHAVE_CPU_FEATURES_H
 else
   NEON := c
 endif

CMakeLists.txt

@@ -54,6 +54,7 @@ if(ANDROID)
   set(WEBP_DEP_INCLUDE_DIRS ${WEBP_DEP_INCLUDE_DIRS}
     ${ANDROID_NDK}/sources/android/cpufeatures
   )
+  add_definitions(-DHAVE_CPU_FEATURES_H)
 endif()
 
 ################################################################################

build.gradle

@@ -84,6 +84,7 @@ model {
       // Check for NEON usage.
       if (getTargetPlatform() == "arm" || getTargetPlatform() == "arm64") {
         NEON = "c.neon"
+        cCompiler.define "HAVE_CPU_FEATURES_H"
       } else {
         NEON = "c"
       }

configure.ac

@@ -243,6 +243,10 @@ AS_IF([test "x$enable_neon" != "xno"], [
           NEON_FLAGS=""],
           [AC_DEFINE(WEBP_HAVE_NEON_RTCD, [1],
                      [Set to 1 if runtime detection of NEON is enabled])])])
+
+      case "$host_os" in
+        *android*) AC_CHECK_HEADERS([cpu-features.h]) ;;
+      esac
       ;;
   esac
   AC_SUBST([NEON_FLAGS])])

src/dsp/dsp.h

@@ -72,18 +72,20 @@ extern "C" {
 #define WEBP_USE_AVX2
 #endif
 
-#if defined(__ANDROID__) && defined(__ARM_ARCH_7A__)
-#define WEBP_ANDROID_NEON  // Android targets that might support NEON
-#endif
-
 // The intrinsics currently cause compiler errors with arm-nacl-gcc and the
 // inline assembly would need to be modified for use with Native Client.
-#if (defined(__ARM_NEON__) || defined(WEBP_ANDROID_NEON) || \
+#if (defined(__ARM_NEON__) || \
      defined(__aarch64__) || defined(WEBP_HAVE_NEON)) && \
     !defined(__native_client__)
 #define WEBP_USE_NEON
 #endif
 
+#if !defined(WEBP_USE_NEON) && defined(__ANDROID__) && \
+    defined(__ARM_ARCH_7A__) && defined(HAVE_CPU_FEATURES_H)
+#define WEBP_ANDROID_NEON  // Android targets that may have NEON
+#define WEBP_USE_NEON
+#endif
+
 #if defined(_MSC_VER) && _MSC_VER >= 1700 && defined(_M_ARM)
 #define WEBP_USE_NEON
 #define WEBP_USE_INTRINSICS