Add minimal stdint

This adds a minimal subset of stdint and stddef that is required by the
runtime.

Signed-off-by: Curtis Millar <curtis@curtism.me>

include/sel4runtime/stddef.h

diff --git a/include/sel4runtime/stddef.h b/include/sel4runtime/stddef.h
new file mode 100644
index 0000000..b001c16
--- /dev/null
+++ b/include/sel4runtime/stddef.h
@@ -0,0 +1,25 @@
+/*
+ * Copyright 2020, Data61
+ * Commonwealth Scientific and Industrial Research Organisation (CSIRO)
+ * ABN 41 687 119 230.
+ *
+ * This software may be distributed and modified according to the terms of
+ * the BSD 2-Clause license. Note that NO WARRANTY is provided.
+ * See "LICENSE_BSD2.txt" for details.
+ *
+ * @TAG(DATA61_BSD)
+ */
+
+#include <sel4runtime/stdint.h>
+
+#pragma once
+
+/*
+ * This is a very naive implementation of stddef that should work for
+ * most major platforms. This is the minimal subset needed for the
+ * runtime.
+ */
+
+typedef sel4runtime_uintptr_t sel4runtime_size_t;
+
+#define SEL4RUNTIME_NULL ((void *)0)

include/sel4runtime/stdint.h

diff --git a/include/sel4runtime/stdint.h b/include/sel4runtime/stdint.h
new file mode 100644
index 0000000..0f21e29
--- /dev/null
+++ b/include/sel4runtime/stdint.h
@@ -0,0 +1,40 @@
+/*
+ * Copyright 2020, Data61
+ * Commonwealth Scientific and Industrial Research Organisation (CSIRO)
+ * ABN 41 687 119 230.
+ *
+ * This software may be distributed and modified according to the terms of
+ * the BSD 2-Clause license. Note that NO WARRANTY is provided.
+ * See "LICENSE_BSD2.txt" for details.
+ *
+ * @TAG(DATA61_BSD)
+ */
+
+#pragma once
+
+/*
+ * This is a very naive implementation of stdint that should work for
+ * most major platforms. This is the minimal subset needed for the
+ * runtime.
+ */
+
+_Static_assert(sizeof(char)      == 1, "char is 8 bits");
+_Static_assert(sizeof(short)     == 2, "short is 16 bits");
+_Static_assert(sizeof(int)       == 4, "int is 32 bits");
+_Static_assert(sizeof(long long) == 8, "long long is 64 bits");
+_Static_assert(sizeof(long)      == sizeof(void *), "long is word size");
+
+/* Fixed size integer types */
+typedef signed char      sel4runtime_int8_t;
+typedef signed short     sel4runtime_int16_t;
+typedef signed int       sel4runtime_int32_t;
+typedef signed long long sel4runtime_int64_t;
+
+typedef unsigned char      sel4runtime_uint8_t;
+typedef unsigned short     sel4runtime_uint16_t;
+typedef unsigned int       sel4runtime_uint32_t;
+typedef unsigned long long sel4runtime_uint64_t;
+
+/* Word-sized integer types */
+typedef signed long   sel4runtime_intptr_t;
+typedef unsigned long sel4runtime_uintptr_t;