Thank you very much Lucas!

Attached is a new netsurf webpage image using dejavu freetpe font.
Most peoples here don't have interest to Japanese font, I show dejavu font example.

Main changes are frontends/framebuffer/font_freetype.c and netsurf/mkfile, and of course
put dejavu font files under /sys/lib/netsurf/fonts/truetype/dejavu.

The font defines in mkfile didn't work, so I hard coded each font names in
font_freetype.c.☺

mkfile:
OBJ=\
...
#	frontends/framebuffer/font_internal.$O \
#	frontends/framebuffer/font-ns-sans.$O \
	frontends/framebuffer/font_freetype.$O \
...
CFLAGS=\
...
	-DNETSURF_FB_FONTPATH="/sys/lib/netsurf/fonts/truetype/dejavu" \
...
	-DFB_USE_FREETYPE \
#	-DNETSURF_FB_FONT_SANS_SERIF =const char *"DejaVuSans.ttf\" \
#	-DNETSURF_FB_FONT_SANS_SERIF_BOLD =const char *"DejaVuSans-Bold.ttf" \
#	-DNETSURF_FB_FONT_SANS_SERIF_ITALIC =const char *"DejaVuSans-Oblique.ttf\" \
#	-DNETSURF_FB_FONT_SANS_SERIF_ITALIC_BOLD =const char *"DejaVuSans-BoldOblique.ttf" \
#	-DNETSURF_FB_FONT_SERIF =const char *"DejaVuSerif.ttf" \
#	-DNETSURF_FB_FONT_SERIF_BOLD =const char *"DejaVuSerif-Bold.ttf" \
#	-DNETSURF_FB_FONT_MONOSPACE =const char *"DejaVuSansMono.ttf" \
#	-DNETSURF_FB_FONT_MONOSPACE_BOLD =const char *"DejaVuSansMono-Bold.ttf" \
#	-DNETSURF_FB_FONT_CURSIVE =const char *"Comic_Sans_MS.ttf" \
#	-DNETSURF_FB_FONT_FANTASY =const char *"Impact.ttf"

font_freetype.c:
...
/* exported interface documented in framebuffer/font.h */
bool fb_font_init(void)
{
...
	/* Start with the sans serif font */
	fb_face = fb_new_face(nsoption_charp(fb_face_sans_serif),
			      "sans_serif.ttf",
//			      NETSURF_FB_FONT_SANS_SERIF);
			     "DejaVuSans.ttf");		/* K.Okamoto */
...
	/* Bold sans serif face */
	fb_face = fb_new_face(nsoption_charp(fb_face_sans_serif_bold),
                            "sans_serif_bold.ttf",
//                            NETSURF_FB_FONT_SANS_SERIF_BOLD);
			  "DejaVuSans-Bold.ttf");		/* K.Okamoto */
...
	/* Italic sans serif face */
	fb_face = fb_new_face(nsoption_charp(fb_face_sans_serif_italic),
			      "sans_serif_italic.ttf",
//			      NETSURF_FB_FONT_SANS_SERIF_ITALIC);
	   		     "DejaVuSans-Oblique.ttf");		/* K.Okamoto */
...
	/* Bold italic sans serif face */
	fb_face = fb_new_face(nsoption_charp(fb_face_sans_serif_italic_bold), 
			      "sans_serif_italic_bold.ttf",
//			      NETSURF_FB_FONT_SANS_SERIF_ITALIC_BOLD);
			     "DejaVuSans-BoldOblique.ttf");		/* K.Okamoto */
...
	/* serif face */
	fb_face = fb_new_face(nsoption_charp(fb_face_serif),
                            "serif.ttf",
//			      NETSURF_FB_FONT_SERIF);
			  "DejaVuSerif.ttf");		/* K.Okamoto */
...
	/* bold serif face*/
	fb_face = fb_new_face(nsoption_charp(fb_face_serif_bold),
			      "serif_bold.ttf",
//			      NETSURF_FB_FONT_SERIF_BOLD);
			      "DejaVuSerif-Bold.ttf");		/* K.Okamoto */
...
	/* monospace face */
	fb_face = fb_new_face(nsoption_charp(fb_face_monospace),
			      "monospace.ttf",
//			      NETSURF_FB_FONT_MONOSPACE);
			      "DejaVuSansMono.ttf");		/* K.Okamoto */
...
	/* bold monospace face*/
	fb_face = fb_new_face(nsoption_charp(fb_face_monospace_bold),
			      "monospace_bold.ttf",
//			      NETSURF_FB_FONT_MONOSPACE_BOLD);
			      "DejaVuSansMono-Bold.ttf");		/* K.Okamoto */
...
	/* cursive face */
	fb_face = fb_new_face(nsoption_charp(fb_face_cursive),
			      "cursive.ttf",
//			      NETSURF_FB_FONT_CURSIVE);
			      "Comic_Sans_MS.ttf");		/* K.Okamoto */
...
	fb_face = fb_new_face(nsoption_charp(fb_face_fantasy),
			      "fantasy.ttf",
//			      NETSURF_FB_FONT_FANTASY);
			     "Impact.ttf");		/* K.Okamoto */
...

Kenji

PS: 
please include two lines in ft2build.h like:
#ifndef FT2BUILD_H_
#define FT2BUILD_H_

#pragma	src	"/sys/ports/ape-libs/libfreetype"
#pragma	lib	"/$M/lib/ape/libfreetype.a"

#include <freetype/config/ftheader.h>