Undefined symbols: _fgetc_unlocked

[ryandesign]

The latest code in the repository does not build on macOS:

/usr/bin/clang word2vec.c -o word2vec -O3 -arch x86_64 -lm -pthread -Wall -funroll-loops
word2vec.c:74:10: warning: implicit declaration of function 'fgetc_unlocked' is invalid in C99 [-Wimplicit-function-declaration]
    ch = fgetc_unlocked(fin);
         ^
1 warning generated.
Undefined symbols for architecture x86_64:
  "_fgetc_unlocked", referenced from:
      _ReadWord in word2vec-f21758.o
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)
make: *** [word2vec] Error 1

[Genie-Liu]

there's a pr to fix this. #40