gnu: unzip: Fix CVE-2014-9636 and some other bugs.

* gnu/packages/patches/unzip-CVE-2014-9636.patch,
  gnu/packages/patches/unzip-allow-greater-hostver-values.patch,
  gnu/packages/patches/unzip-increase-size-of-cfactorstr.patch,
  gnu/packages/patches/unzip-initialize-symlink-flag.patch,
  gnu/packages/patches/unzip-remove-build-date.patch: New files.
* gnu-system.am (dist_patch_DATA): Add them.
* gnu/packages/zip.scm (unzip)[source]: Add patches.
  [arguments]: Use 'modify-phases'.  Remove custom 'configure' phase; pass
  additional make-flags instead.  Add custom 'build' phase that builds
  "generic_gcc" target; remove "generic_gcc" from make-flags.

gnu/packages/patches/unzip-initialize-symlink-flag.patch

@@ -0,0 +1,22 @@
+Copied from Debian.
+
+From: Andreas Schwab <schwab@linux-m68k.org>
+Subject: Initialize the symlink flag
+Bug-Debian: http://bugs.debian.org/717029
+X-Debian-version: 6.0-10
+
+--- a/process.c
++++ b/process.c
+@@ -1758,6 +1758,12 @@
+         = (G.crec.general_purpose_bit_flag & (1 << 11)) == (1 << 11);
+ #endif
+ 
++#ifdef SYMLINKS
++    /* Initialize the symlink flag, may be set by the platform-specific
++       mapattr function.  */
++    G.pInfo->symlink = 0;
++#endif
++
+     return PK_COOL;
+ 
+ } /* end function process_cdir_file_hdr() */