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).

src/libtemple/libtemple.cpp

@@ -74,4 +74,8 @@ long time_jiffies() { return 0; }
 
 long time_now() { return 0; }
 
-void time_sleep(long duration) { }
+void time_sleep(long duration) { }
+
+void* truetype_malloc(int size) { return 0; }
+
+void truetype_free(void* ptr) { }

src/truetype/stb_truetype.h

@@ -468,8 +468,8 @@ int main(int arg, char **argv)
    // #define your own functions "STBTT_malloc" / "STBTT_free" to avoid malloc.h
    #ifndef STBTT_malloc
    #include <stdlib.h>
-   #define STBTT_malloc(x,u)  ((void)(u),malloc(x))
-   #define STBTT_free(x,u)    ((void)(u),free(x))
+   #define STBTT_malloc(x,u)  ((void)(u),_Z15truetype_malloci(x))
+   #define STBTT_free(x,u)    ((void)(u),_Z13truetype_freePv(x))
    #endif
 
    #ifndef STBTT_assert

src/truetype/truetype.c

@@ -1,3 +1,6 @@
+void* _Z15truetype_malloci(int size);
+void _Z13truetype_freePv(void* ptr);
+
 #define STB_TRUETYPE_IMPLEMENTATION
 #include "stb_truetype.h"
 
@@ -5,7 +8,8 @@ unsigned char* stbtt_RenderText(stbtt_fontinfo* info, int b_w, int b_h, int l_h,
 {
     // https://github.com/justinmeiners/stb-truetype-example
     /* create a bitmap for the phrase */
-    unsigned char* bitmap = calloc(b_w * b_h, sizeof(unsigned char));
+    unsigned char* bitmap = STBTT_malloc(b_w * b_h, sizeof(unsigned char));
+    memset(bitmap, 0, b_w * b_h);
 
     /* calculate font scaling */
     float scale = stbtt_ScaleForPixelHeight(info, l_h);