third_party: Add support for building libffi for ARM.

third_party/libffi/include/arm-unknown-linux-gnu/fficonfig.h

Index: third_party/libffi/include/arm-unknown-linux-gnu/fficonfig.h
diff --git a/third_party/libffi/include/x86_64-unknown-linux-gnu/fficonfig.h b/third_party/libffi/include/arm-unknown-linux-gnu/fficonfig.h
similarity index 95%
copy from third_party/libffi/include/x86_64-unknown-linux-gnu/fficonfig.h
copy to third_party/libffi/include/arm-unknown-linux-gnu/fficonfig.h
index a70cf52a91f4672a376c46e0ab36a39641636009..d7a3f446cc8f93891e0d43b77b45df89039e6fdc 100644
--- a/third_party/libffi/include/x86_64-unknown-linux-gnu/fficonfig.h
+++ b/third_party/libffi/include/arm-unknown-linux-gnu/fficonfig.h
@@ -13,7 +13,7 @@
 /* #undef C_ALLOCA */
 
 /* Define to the flags needed for the .section .eh_frame directive. */
-#define EH_FRAME_FLAGS "a"
+#define EH_FRAME_FLAGS "aw"
 
 /* Define this if you want extra debugging. */
 /* #undef FFI_DEBUG */
@@ -41,7 +41,7 @@
 #define HAVE_ALLOCA_H 1
 
 /* Define if your assembler supports .ascii. */
-#define HAVE_AS_ASCII_PSEUDO_OP 1
+/* #undef HAVE_AS_ASCII_PSEUDO_OP */
 
 /* Define if your assembler supports .cfi_* directives. */
 #define HAVE_AS_CFI_PSEUDO_OP 1
@@ -54,13 +54,13 @@
 /* #undef HAVE_AS_SPARC_UA_PCREL */
 
 /* Define if your assembler supports .string. */
-#define HAVE_AS_STRING_PSEUDO_OP 1
+/* #undef HAVE_AS_STRING_PSEUDO_OP */
 
 /* Define if your assembler supports unwind section type. */
-#define HAVE_AS_X86_64_UNWIND_SECTION_TYPE 1
+/* #undef HAVE_AS_X86_64_UNWIND_SECTION_TYPE */
 
 /* Define if your assembler supports PC relative relocs. */
-#define HAVE_AS_X86_PCREL 1
+/* #undef HAVE_AS_X86_PCREL */
 
 /* Define to 1 if you have the <dlfcn.h> header file. */
 #define HAVE_DLFCN_H 1
@@ -72,7 +72,7 @@
 #define HAVE_INTTYPES_H 1
 
 /* Define if you have the long double type and it is bigger than a double */
-#define HAVE_LONG_DOUBLE 1
+/* #undef HAVE_LONG_DOUBLE */
 
 /* Define if you support more than one size of the long double type */
 /* #undef HAVE_LONG_DOUBLE_VARIANT */
@@ -99,7 +99,7 @@
 #define HAVE_MMAP_FILE 1
 
 /* Define if .eh_frame sections should be read-only. */
-#define HAVE_RO_EH_FRAME 1
+/* #undef HAVE_RO_EH_FRAME */
 
 /* Define to 1 if you have the <stdint.h> header file. */
 #define HAVE_STDINT_H 1
@@ -154,10 +154,10 @@
 #define SIZEOF_DOUBLE 8
 
 /* The size of `long double', as computed by sizeof. */
-#define SIZEOF_LONG_DOUBLE 16
+#define SIZEOF_LONG_DOUBLE 8
 
 /* The size of `size_t', as computed by sizeof. */
-#define SIZEOF_SIZE_T 8
+#define SIZEOF_SIZE_T 4
 
 /* If using the C implementation of alloca, define if you know the
    direction of stack growth for your system; otherwise it will be