Add custom getcontext() implementation for Android.

src/common/android/include/sys/ucontext.h

Index: src/common/android/include/sys/ucontext.h
===================================================================
--- src/common/android/include/sys/ucontext.h	(revision 1022)
+++ src/common/android/include/sys/ucontext.h	(working copy)
@@ -50,11 +50,15 @@
 #include <asm/sigcontext.h>
 typedef struct sigcontext mcontext_t;
 
+// The ARM kernel uses a 64-bit signal mask.
+typedef uint32_t  kernel_sigmask_t[2];
+
 typedef struct ucontext {
   uint32_t uc_flags;
   struct ucontext* uc_link;
   stack_t uc_stack;
   mcontext_t uc_mcontext;
+  kernel_sigmask_t uc_sigmask;
   // Other fields are not used by Google Breakpad. Don't define them.
 } ucontext_t;
 
@@ -110,12 +114,16 @@
   REG_SS,
 };
 
+// The i386 kernel uses a 64-bit signal mask.
+typedef uint32_t kernel_sigmask_t[2];
+
 typedef struct ucontext {
   uint32_t uc_flags;
   struct ucontext* uc_link;
   stack_t uc_stack;
   mcontext_t uc_mcontext;
-  // Other fields are not used by Google Breakpad. Don't define them.
+  kernel_sigmask_t uc_sigmask;
+  struct _libc_fpstate __fpregs_mem;
 } ucontext_t;
 
 #elif defined(__mips__)
@@ -142,11 +150,15 @@
   uint32_t lo3;
 } mcontext_t;
 
+// The MIPS kernel uses a 128-bit signal mask.
+typedef uint32_t kernel_sigmask_t[4];
+
 typedef struct ucontext {
   uint32_t uc_flags;
   struct ucontext* uc_link;
   stack_t uc_stack;
   mcontext_t uc_mcontext;
+  kernel_sigmask_t uc_sigmask;
   // Other fields are not used by Google Breakpad. Don't define them.
 } ucontext_t;