Fails to build with error: ‘memcpy’ was not declared in this scope

[shrx]

Building with gcc 6, make fails with:

guetzli.cc
guetzli/guetzli.cc: In function ‘bool {anonymous}::ReadPNG(FILE*, int*, int*, std::vector<unsigned char>*)’:
guetzli/guetzli.cc:119:45: error: ‘memcpy’ was not declared in this scope
         memcpy(row_out, row_in, 3 * (*xsize));
                                             ^
guetzli/guetzli.cc: In function ‘int main(int, char**)’:
guetzli/guetzli.cc:221:68: error: ‘memcmp’ was not declared in this scope
       memcmp(in_data.data(), kPNGMagicBytes, sizeof(kPNGMagicBytes)) == 0) {
                                                                    ^
guetzli.make:165: recipe for target 'obj/Release/guetzli.o' failed
make[1]: *** [obj/Release/guetzli.o] Error 1
Makefile:28: recipe for target 'guetzli' failed
make: *** [guetzli] Error 2