No, it's in the core:
C:\Program Files (x86)\Arduino\hardware\arduino\avr\cores\arduino\binary.h
#ifndef Binary_h
#define Binary_h
#define B0 0
#define B00 0
#define B000 0
#define B0000 0
#define B00000 0
#define B000000 0
#define B0000000 0
#define B00000000 0
#define B1 1
#define B01 1
#define B001 1
#define B0001 1
#define B00001 1
#define B000001 1
#define B0000001 1
#define B00000001 1
#define B10 2
#define B010 2
#define B0010 2
#define B00010 2
#define B000010 2
#define B0000010 2
#define B00000010 2
#define B11 3
#define B011 3
#define B0011 3
#define B00011 3
#define B000011 3
#define B0000011 3
#define B00000011 3
#define B100 4
#define B0100 4
#define B00100 4
#define B000100 4
#define B0000100 4
#define B00000100 4
#define B101 5
#define B0101 5
#define B00101 5
#define B000101 5
#define B0000101 5
#define B00000101 5
#define B110 6
#define B0110 6
#define B00110 6
#define B000110 6
#define B0000110 6
#define B00000110 6
#define B111 7
#define B0111 7
#define B00111 7
#define B000111 7
#define B0000111 7
#define B00000111 7
#define B1000 8
#define B01000 8
#define B001000 8
#define B0001000 8
#define B00001000 8
#define B1001 9
#define B01001 9
#define B001001 9
#define B0001001 9
#define B00001001 9
#define B1010 10
#define B01010 10
#define B001010 10
#define B0001010 10
#define B00001010 10
#define B1011 11
#define B01011 11
#define B001011 11
#define B0001011 11
#define B00001011 11
#define B1100 12
#define B01100 12
#define B001100 12
#define B0001100 12
#define B00001100 12
#define B1101 13
#define B01101 13
#define B001101 13
#define B0001101 13
#define B00001101 13
#define B1110 14
#define B01110 14
#define B001110 14
#define B0001110 14
#define B00001110 14
#define B1111 15
#define B01111 15
#define B001111 15
#define B0001111 15
#define B00001111 15
#define B10000 16
#define B010000 16
#define B0010000 16
#define B00010000 16
#define B10001 17
#define B010001 17
#define B0010001 17
#define B00010001 17
#define B10010 18
#define B010010 18
#define B0010010 18
#define B00010010 18
#define B10011 19
#define B010011 19
#define B0010011 19
#define B00010011 19
#define B10100 20
#define B010100 20
#define B0010100 20
#define B00010100 20
#define B10101 21
#define B010101 21
#define B0010101 21
#define B00010101 21
#define B10110 22
#define B010110 22
#define B0010110 22
#define B00010110 22
#define B10111 23
#define B010111 23
#define B0010111 23
#define B00010111 23
#define B11000 24
#define B011000 24
#define B0011000 24
#define B00011000 24
#define B11001 25
#define B011001 25
#define B0011001 25
#define B00011001 25
#define B11010 26
#define B011010 26
#define B0011010 26
#define B00011010 26
#define B11011 27
#define B011011 27
#define B0011011 27
#define B00011011 27
#define B11100 28
#define B011100 28
#define B0011100 28
#define B00011100 28
#define B11101 29
#define B011101 29
#define B0011101 29
#define B00011101 29
#define B11110 30
#define B011110 30
#define B0011110 30
#define B00011110 30
#define B11111 31
#define B011111 31
#define B0011111 31
#define B00011111 31
#define B100000 32
#define B0100000 32
#define B00100000 32
#define B100001 33
#define B0100001 33
#define B00100001 33
#define B100010 34
#define B0100010 34
#define B00100010 34
#define B100011 35
#define B0100011 35
#define B00100011 35
#define B100100 36
#define B0100100 36
#define B00100100 36
#define B100101 37
#define B0100101 37
#define B00100101 37
#define B100110 38
#define B0100110 38
#define B00100110 38
#define B100111 39
#define B0100111 39
#define B00100111 39
#define B101000 40
#define B0101000 40
... and so on and so on and blah blah blah...
#endif
It's probably the most totally useless and stupid thing I've ever seen in there. How is B0011 better than 0b0011? It's the same thing!
On top of that, they only define out to 8 bits. The 0b prefix is part of the language and not limited in the same way.
EDIT: Ignore my ignorant rambling, see CrossRoads's reply below.