Add x86 missing feature detections for ndk_compat (#58)

One more step towards #47.
diff --git a/include/cpuinfo_x86.h b/include/cpuinfo_x86.h
index 13bcdf4..bb61293 100644
--- a/include/cpuinfo_x86.h
+++ b/include/cpuinfo_x86.h
@@ -20,6 +20,7 @@
 CPU_FEATURES_START_CPP_NAMESPACE
 
 // See https://en.wikipedia.org/wiki/CPUID for a list of x86 cpu features.
+// The field names are based on the short name provided in the wikipedia tables.
 typedef struct {
   int aes : 1;
   int erms : 1;
@@ -55,6 +56,10 @@
   int smx : 1;
   int sgx : 1;
   int cx16 : 1;  // aka. CMPXCHG16B
+  int sha : 1;
+  int popcnt : 1;
+  int movbe : 1;
+  int rdrnd : 1;
 
   // Make sure to update X86FeaturesEnum below if you add a field here.
 } X86Features;
@@ -140,6 +145,10 @@
   X86_SMX,
   X86_SGX,
   X86_CX16,
+  X86_SHA,
+  X86_POPCNT,
+  X86_MOVBE,
+  X86_RDRND,
   X86_LAST_,
 } X86FeaturesEnum;