Make deps: Fix zlib symbols defined twice

We compile zlib as own dependency, but are not informing BLOSC
to use it. This leads to zlib symbols defined twice when linking
Blender: one set comes from libz.a and another one from libblosc.a.

Tested on Linux Debian testing and CentOS 7.5.

It is possible that this change on its own will lead to linking
errors after libraries are re-compiled, This will be fixed as
a dedicated fix to Blender's build system.

Reviewed By: brecht, mont29, LazyDodo

Differential Revision: https://developer.blender.org/D6641

build_files/build_environment/cmake/blosc.cmake

@@ -29,13 +29,11 @@ set(BLOSC_EXTRA_ARGS
   -DCMAKE_POSITION_INDEPENDENT_CODE=ON
 )
 
-if(WIN32)
 # Prevent blosc from including it's own local copy of zlib in the object file
 # and cause linker errors with everybody else.
 set(BLOSC_EXTRA_ARGS ${BLOSC_EXTRA_ARGS}
   -DPREFER_EXTERNAL_ZLIB=ON
 )
-endif()
 
 ExternalProject_Add(external_blosc
   URL ${BLOSC_URI}

build_files/build_environment/patches/blosc.diff

@@ -10,6 +10,70 @@ diff -Naur src/blosc/CMakeLists.txt external_blosc/blosc/CMakeLists.txt
      endif(NOT Threads_FOUND)
  else(WIN32)
      find_package(Threads REQUIRED)
+diff -Naur src/CMakeLists.txt external_blosc/CMakeLists.txt
+--- src/CMakeLists.txt	2016-02-03 10:26:28 -0700
++++ external_blosc/CMakeLists.txt	2017-03-03 09:03:31 -0700
+@@ -17,8 +17,8 @@
+ #       do not include support for the Snappy library
+ #   DEACTIVATE_ZLIB: default OFF
+ #       do not include support for the Zlib library
+-#   PREFER_EXTERNAL_COMPLIBS: default ON
+-#       when found, use the installed compression libs instead of included sources
++#   PREFER_EXTERNAL_ZLIB: default ON
++#       when found, use the installed zlib instead of included sources
+ #   TEST_INCLUDE_BENCH_SINGLE_1: default ON
+ #       add a test that runs the benchmark program passing "single" with 1 thread
+ #       as first parameter
+@@ -80,29 +80,23 @@
+     "Do not include support for the SNAPPY library." OFF)
+ option(DEACTIVATE_ZLIB
+     "Do not include support for the ZLIB library." OFF)
+-option(PREFER_EXTERNAL_COMPLIBS
+-    "When found, use the installed compression libs instead of included sources." ON)
++option(PREFER_EXTERNAL_ZLIB
++    "When found, use the installed zlib instead of included sources." ON)
+ 
+ set(CMAKE_MODULE_PATH "${CMAKE_SOURCE_DIR}/cmake")
+ 
+-if(NOT PREFER_EXTERNAL_COMPLIBS)
++if(NOT PREFER_EXTERNAL_ZLIB)
+     message(STATUS "Finding external libraries disabled.  Using internal sources.")
+-endif(NOT PREFER_EXTERNAL_COMPLIBS)
++endif(NOT PREFER_EXTERNAL_ZLIB)
+ 
+ 
+ if(NOT DEACTIVATE_LZ4)
+-    if(PREFER_EXTERNAL_COMPLIBS)
+-        find_package(LZ4)
+-    endif(PREFER_EXTERNAL_COMPLIBS)
+     # HAVE_LZ4 will be set to true because even if the library is
+     # not found, we will use the included sources for it
+     set(HAVE_LZ4 TRUE)
+ endif(NOT DEACTIVATE_LZ4)
+ 
+ if(NOT DEACTIVATE_SNAPPY)
+-    if(PREFER_EXTERNAL_COMPLIBS)
+-        find_package(Snappy)
+-    endif(PREFER_EXTERNAL_COMPLIBS)
+     # HAVE_SNAPPY will be set to true because even if the library is not found,
+     # we will use the included sources for it
+     set(HAVE_SNAPPY TRUE)
+@@ -110,13 +104,13 @@
+ 
+ if(NOT DEACTIVATE_ZLIB)
+     # import the ZLIB_ROOT environment variable to help finding the zlib library
+-    if(PREFER_EXTERNAL_COMPLIBS)
++    if(PREFER_EXTERNAL_ZLIB)
+         set(ZLIB_ROOT $ENV{ZLIB_ROOT})
+         find_package( ZLIB )
+         if (NOT ZLIB_FOUND )
+             message(STATUS "No zlib found.  Using internal sources.")
+         endif (NOT ZLIB_FOUND )
+-    endif(PREFER_EXTERNAL_COMPLIBS)
++    endif(PREFER_EXTERNAL_ZLIB)
+     # HAVE_ZLIB will be set to true because even if the library is not found,
+     # we will use the included sources for it
+     set(HAVE_ZLIB TRUE)
 diff -Naur external_blosc.orig/blosc/blosc.c external_blosc/blosc/blosc.c
 --- external_blosc.orig/blosc/blosc.c   2018-07-30 04:56:38 -0600
 +++ external_blosc/blosc/blosc.c        2018-08-11 15:27:26 -0600