thirdparty: fix compilation of programs using miniz.h on OpenBSD

[lcheylus]

Fix #22253

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Tests OK on OpenBSD/amd64 with tcc

$ ./v -showcc cmd/tools/vcompress.v
> C compiler cmd: '/home/fox/dev/vlang.git/thirdparty/tcc/tcc.exe' '@/tmp/v_1000/vcompress.01J82Q6J8AJ8YDG0VEP89BQA6S.tmp.c.rsp'
> C compiler response file "/tmp/v_1000/vcompress.01J82Q6J8AJ8YDG0VEP89BQA6S.tmp.c.rsp":
  -o "/home/fox/dev/vlang.git/cmd/tools/vcompress" -D GC_BUILTIN_ATOMIC=1 -D GC_THREADS=1 -I "/usr/local/include" -I "/home/fox/dev/vlang.git/thirdparty/zip" "/tmp/v_1000/vcompress.01J82Q6J8AJ8YDG0VEP89BQA6S.tmp.c" -std=c99 -D_DEFAULT_SOURCE -bt25 "/usr/local/lib/libgc.a" -lgc -lpthread

$ ./cmd/tools/vcompress
v compress <type> <in> <out>
supported types: zlib