Add zlib gzip functions

These will now be included in the cosmopolitan.a releases. It took a bit
of time because, these functions depend on heavyweight parts of the libc
that wouldn't be appropriate for the core zlib library to depend upon.

Fixes #345

third_party/zlib/gz/gzguts.inc

@@ -0,0 +1,115 @@
+#include "libc/errno.h"
+#include "libc/limits.h"
+#include "libc/str/str.h"
+#include "third_party/zlib/zlib.h"
+// clang-format off
+
+/* gzguts.h -- zlib internal header definitions for gz* operations
+ * Copyright (C) 2004, 2005, 2010, 2011, 2012, 2013, 2016 Mark Adler
+ * For conditions of distribution and use, see copyright notice in zlib.h
+ */
+
+#ifdef _LARGEFILE64_SOURCE
+#  ifndef _LARGEFILE_SOURCE
+#    define _LARGEFILE_SOURCE 1
+#  endif
+#  ifdef _FILE_OFFSET_BITS
+#    undef _FILE_OFFSET_BITS
+#  endif
+#endif
+
+#define ZLIB_INTERNAL __attribute__((visibility ("hidden")))
+#define _POSIX_SOURCE
+
+#if defined(STDC99) || (defined(__TURBOC__) && __TURBOC__ >= 0x550)
+#  ifndef HAVE_VSNPRINTF
+#    define HAVE_VSNPRINTF
+#  endif
+#endif
+
+/* since "static" is used to mean two completely different things in C, we
+   define "local" for the non-static meaning of "static", for readability
+   (compile with -Dlocal if your debugger can't find static symbols) */
+
+#define zstrerror() strerror(errno)
+
+/* provide prototypes for these when building zlib without LFS */
+#if !defined(_LARGEFILE64_SOURCE) || _LFS64_LARGEFILE-0 == 0
+    gzFile gzopen64(const char *, const char *);
+    int64_t gzseek64(gzFile, int64_t, int);
+    int64_t gztell64(gzFile);
+    int64_t gzoffset64(gzFile);
+#endif
+
+/* default memLevel */
+#if MAX_MEM_LEVEL >= 8
+#  define DEF_MEM_LEVEL 8
+#else
+#  define DEF_MEM_LEVEL  MAX_MEM_LEVEL
+#endif
+
+/* default i/o buffer size -- double this for output when reading (this and
+   twice this must be able to fit in an unsigned type) */
+#define GZBUFSIZE 8192
+
+/* gzip modes, also provide a little integrity check on the passed structure */
+#define GZ_NONE 0
+#define GZ_READ 7247
+#define GZ_WRITE 31153
+#define GZ_APPEND 1     /* mode set to GZ_WRITE after the file is opened */
+
+/* values for gz_state how */
+#define LOOK 0      /* look for a gzip header */
+#define COPY 1      /* copy input directly */
+#define GZIP 2      /* decompress a gzip stream */
+
+/* internal gzip file state data structure */
+typedef struct {
+        /* exposed contents for gzgetc() macro */
+    struct gzFile_s x;      /* "x" for exposed */
+                            /* x.have: number of bytes available at x.next */
+                            /* x.next: next output data to deliver or write */
+                            /* x.pos: current position in uncompressed data */
+        /* used for both reading and writing */
+    int mode;               /* see gzip modes above */
+    int fd;                 /* file descriptor */
+    char *path;             /* path or fd for error messages */
+    unsigned size;          /* buffer size, zero if not allocated yet */
+    unsigned want;          /* requested buffer size, default is GZBUFSIZE */
+    unsigned char *in;      /* input buffer (double-sized when writing) */
+    unsigned char *out;     /* output buffer (double-sized when reading) */
+    int direct;             /* 0 if processing gzip, 1 if transparent */
+        /* just for reading */
+    int how;                /* 0: get header, 1: copy, 2: decompress */
+    int64_t start;        /* where the gzip data started, for rewinding */
+    int eof;                /* true if end of input file reached */
+    int past;               /* true if read requested past end */
+        /* just for writing */
+    int level;              /* compression level */
+    int strategy;           /* compression strategy */
+        /* seek request */
+    int64_t skip;         /* amount to skip (already rewound if backwards) */
+    int seek;               /* true if seek request pending */
+        /* error information */
+    int err;                /* error code */
+    char *msg;              /* error message */
+        /* zlib inflate or deflate stream */
+    z_stream strm;          /* stream structure in-place (not a pointer) */
+} gz_state;
+typedef gz_state *gz_statep;
+
+/* shared functions */
+void ZLIB_INTERNAL gz_error (gz_statep, int, const char *);
+#if defined UNDER_CE
+char ZLIB_INTERNAL *gz_strwinerror (DWORD error);
+#endif
+
+/* GT_OFF(x), where x is an unsigned value, is true if x > maximum int64_t
+   value -- needed when comparing unsigned to int64_t, which is signed
+   (possible int64_t types off_t, off64_t, and long are all signed) */
+#ifdef INT_MAX
+#  define GT_OFF(x) (sizeof(int) == sizeof(int64_t) && (x) > INT_MAX)
+#else
+unsigned ZLIB_INTERNAL gz_intmax (void);
+#  define GT_OFF(x) (sizeof(int) == sizeof(int64_t) && (x) > gz_intmax())
+#endif