Administrator@WIN-J4M9KOMET5D  /c/jenkins/workspace/win64/zlib-1.2.11
$ ./configure --64
Checking for gcc...
Checking for shared library support...
Building shared library libz.so.1.2.11 with gcc.
Checking for size_t... Yes.
Checking for off64_t... No.
Checking for fseeko... Yes.
Checking for strerror... Yes.
Checking for unistd.h... Yes.
Checking for stdarg.h... Yes.
Checking whether to use vs[n]printf() or s[n]printf()... using vs[n]printf().
Checking for vsnprintf() in stdio.h... Yes.
Checking for return value of vsnprintf()... Yes.
Checking for attribute(visibility) support... No.

Administrator@WIN-J4M9KOMET5D  /c/jenkins/workspace/win64/zlib-1.2.11
$ make -f win32/Makefile.gcc
gcc  -O3 -Wall -c -o adler32.o adler32.c
gcc  -O3 -Wall -c -o compress.o compress.c
gcc  -O3 -Wall -c -o crc32.o crc32.c
gcc  -O3 -Wall -c -o deflate.o deflate.c
gcc  -O3 -Wall -c -o gzclose.o gzclose.c
gcc  -O3 -Wall -c -o gzlib.o gzlib.c
gzlib.c: In function 'gz_open':
gzlib.c:243:20: warning: implicit declaration of function '_wopen' [-Wimplicit-function-declaration]
         fd == -2 ? _wopen(path, oflag, 0666) :
                    ^~~~~~
gcc  -O3 -Wall -c -o gzread.o gzread.c
gcc  -O3 -Wall -c -o gzwrite.o gzwrite.c
gcc  -O3 -Wall -c -o infback.o infback.c
gcc  -O3 -Wall -c -o inffast.o inffast.c
gcc  -O3 -Wall -c -o inflate.o inflate.c
gcc  -O3 -Wall -c -o inftrees.o inftrees.c
gcc  -O3 -Wall -c -o trees.o trees.c
gcc  -O3 -Wall -c -o uncompr.o uncompr.c
gcc  -O3 -Wall -c -o zutil.o zutil.c
ar rcs libz.a adler32.o compress.o crc32.o deflate.o gzclose.o gzlib.o gzread.o gzwrite.o infback.o inffast.o inflate.o
inftrees.o trees.o uncompr.o zutil.o
gcc -shared -Wl,--out-implib,libz.dll.a  \
-o zlib1.dll win32/zlib.def adler32.o compress.o crc32.o deflate.o gzclose.o gzlib.o gzread.o gzwrite.o infback.o inffas
t.o inflate.o inftrees.o trees.o uncompr.o zutil.o  zlibrc.o
gzlib.o:gzlib.c:(.text+0xa4b): undefined reference to `_wopen'
gzlib.o:gzlib.c:(.text+0xa4b): relocation truncated to fit: R_X86_64_PC32 against undefined symbol `_wopen'
gzlib.o:gzlib.c:(.text+0xbf9): undefined reference to `_wopen'
gzlib.o:gzlib.c:(.text+0xbf9): relocation truncated to fit: R_X86_64_PC32 against undefined symbol `_wopen'
collect2: error: ld returned 1 exit status
make: *** [win32/Makefile.gcc:96: zlib1.dll] Error 1

Administrator@WIN-J4M9KOMET5D  /c/jenkins/workspace/win64/zlib-1.2.11
$ gcc -dumpmachine
x86_64-pc-msys

Administrator@WIN-J4M9KOMET5D  /c/jenkins/workspace/win64/zlib-1.2.11