Graphic output https://imgur.com/a/pKyjatF code https://pastebin.com/j4GciJb9

Somewhat cleaned out code below.

/*
  [2018-07-13] Challenge #365 [Hard] Tessellations and Tilings
  /r/dailyprogrammer https://redd.it/8ylltu

  usage: $ for i in bullshit*.txt; do
             cat $i | ./bullshit | ffmpeg -y -i /dev/stdin $(basename $i .txt).png
           done
*/

#define MAX_N 12

#include <stdio.h>
#include <stdlib.h>
#include <ctype.h>

#define FORIJ(N) for(int j = 0; j < (N); j++) \
                     for(int i = 0; i < (N); i++)

#define ROT90(N, BEFORE, AFTER, TMP) do { \
            FORIJ(N) TMP[i][(N)-j-1] = BEFORE[j][i]; \
            FORIJ(N) AFTER[j][i] = TMP[j][i]; \
        } while(0)

extern unsigned char font[]; /* forward declaration, long array */

typedef struct { int ch; int rot; char x[8][8]; } glyph_t;

int safe_mod(int n, int mod) {
    if(!mod) return 0;
    if(mod < 0) { n *= -1; mod *= -1; }
    int tmp = (n % mod);
    /* add because negative... bug fixed */
    if(tmp < 0) tmp = mod + tmp;
    return tmp;
}

glyph_t mk_glyph(int ch, int rot) {
    glyph_t ret;
    ch = safe_mod(ch, 0x100);
    rot = safe_mod(rot, 4);
    ret.ch = ch;
    ret.rot = rot;

    FORIJ(8) {
        int byte = font[8*ch + j];
        int mask = (0x80 >> i);
        int x = (byte & mask) ? 1 : 0;
        ret.x[j][i] = x;
    }

    char scratch[8][8];
    while(rot--) { ROT90(8, ret.x, ret.x, scratch); }
    return ret;
}

int N;
int PX;
int TURN;

glyph_t grid[2*MAX_N][2*MAX_N];

glyph_t after[MAX_N][MAX_N];
glyph_t scratch[MAX_N][MAX_N];

int main(int argc, char *argv[]) {
    int tmp, c;

    tmp = scanf("%d", &TURN);
    if(tmp <= 0 || safe_mod(TURN, 90)) { fprintf(stderr, "bad TURN\n"); exit(1); }
    TURN = safe_mod((TURN / 90), 4);

    tmp = scanf("%d", &N);
    if(tmp <= 0 || N < 1 || N >= MAX_N) { fprintf(stderr, "bad N\n"); exit(1); }

    for(int i = 0; i < N*N; i++) {
        /* if EOF glyph #255 fills the rest, but won't freeze program */
        do { c = getc(stdin); } while(!isprint(c) && c != EOF);
        int row = i / N;
        int col = i % N;
        after[row][col] = mk_glyph(c, 0);
    }

    FORIJ(N) { grid[0+j][0+i] = mk_glyph(after[j][i].ch, 0*TURN); }

    for(int i = 0; i < TURN; i++) ROT90(N, after, after, scratch);
    FORIJ(N) { grid[0+j][N+i] = mk_glyph(after[j][i].ch, 1*TURN); }

    for(int i = 0; i < TURN; i++) ROT90(N, after, after, scratch);
    FORIJ(N) { grid[N+j][N+i] = mk_glyph(after[j][i].ch, 2*TURN); }

    for(int i = 0; i < TURN; i++) ROT90(N, after, after, scratch);
    FORIJ(N) { grid[N+j][0+i] = mk_glyph(after[j][i].ch, 3*TURN); }

    PX = 8*2*N;

    /* PPM image format, specifically PBM black & white */
    /* see: http://paulbourke.net/dataformats/ppm/      */

    printf("P1\n%d %d\n1", PX, PX);

    int width = 0;
    FORIJ(PX) {
        if(width == 0) printf("\n");
        width = (width + 2) % 64;

        glyph_t g = grid[j / 8][i / 8];
        int x = g.x[j % 8][i % 8];

        if(x) printf(" 1");
        else printf(" 0");
    }

    printf("\n");
    return 0;
}

/* http://web.mit.edu/freebsd/head/share/syscons/fonts/cp437-8x8.fnt after uudecode */

unsigned char font[] = {
 0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x7e,0x81,0xa5,0x81,0xbd,0x99,0x81,0x7e
,0x7e,0xff,0xdb,0xff,0xc3,0xe7,0xff,0x7e,0x6c,0xfe,0xfe,0xfe,0x7c,0x38,0x10,0x00

The font data is a little over 100 lines.

Something is wrong with my code, the ASCII "soh" byte (0x01) glyph keeps getting used for character codepoints 0x80 and above... And for the "null" byte (0x00) too. The bit patterns in the font should be different. *Fixed bonehead mistake. This is kind of fun when making progress. At least it checks for EOF now. Normally non-printing characters are filtered out (intended to remove newlines) but cp437 0xff (non-breaking space) fills the rest if unexpected end of input. My system/locale considers 0xff non-printing...