Everywhere: Give stbtt its own 32MB static memory pool

At boot time, we preallocate 32MB of RAM to reuse for all malloc()
requests by stbtt_RenderText(), which should be more than enough for the
primary use case (browsing web pages).

System/FFI/TrueType.HC

@@ -0,0 +1,31 @@
+U64 stbtt_heap = MAlloc(1048576 * 32);
+U64 stbtt_pos = 0;
+
+U64 @stbtt_malloc(I64 size)
+{
+    //"stbtt_malloc(%d)\n", size;
+    U64 ptr = stbtt_heap + stbtt_pos;
+    stbtt_pos += size;
+    return ptr;
+}
+
+U0 @stbtt_free(U8* ptr)
+{
+    //"stbtt_free(0x%08x)\n", ptr;
+}
+
+U0 _Z15truetype_malloci()
+{
+    PUSH_SYSV_REGS
+    GET_SYSV_ARGS
+    @stbtt_malloc(p0);
+    POP_SYSV_REGS
+}
+
+U0 _Z13truetype_freePv()
+{
+    PUSH_SYSV_REGS
+    GET_SYSV_ARGS
+    @stbtt_free(p0);
+    POP_SYSV_REGS
+}