[CMake] Simplify zlib inclusion

This commit puts the zlib library search in the toplevel CMakeLists
file, along with other library requirements.

This allows us to remove it from all the other CMakeLists files.

CMakeLists.txt

@@ -170,6 +170,12 @@ set(Boost_USE_MULTITHREADED ON)
 set(Boost_USE_STATIC_RUNTIME OFF)
 find_package(Boost 1.65.0 COMPONENTS filesystem)
 
+# ============================================================================
+# Look for Zlib
+# ============================================================================
+find_package(ZLIB REQUIRED)
+
+
 # ============================================================================
 # Get GNU standard installation directories (GNUInstallDirs module)
 # ============================================================================

src/CMakeLists.txt

@@ -7,13 +7,6 @@ if (with-post-treatments)
   add_subdirectory(post_treatments)
 endif()
 
-
-# ============================================================================
-# Find packages
-# ============================================================================
-find_package(ZLIB REQUIRED)
-
-
 # ============================================================================
 # Add targets add their dependencies
 # ============================================================================

src/libaevol/CMakeLists.txt

@@ -3,12 +3,6 @@
 # ============================================================================
 add_subdirectory(SFMT-src-1.4)
 
-
-# ============================================================================
-# Find packages
-# ============================================================================
-find_package(ZLIB REQUIRED)
-
 # ============================================================================
 # Add targets add their dependencies
 # ============================================================================

src/libaevol/SFMT-src-1.4/CMakeLists.txt

-# ============================================================================
-# Find packages
-# ============================================================================
-find_package(ZLIB REQUIRED)
-
 # ============================================================================
 # Add targets add their dependencies
 # ============================================================================

src/post_treatments/CMakeLists.txt

@@ -2,11 +2,6 @@
 # Tell cmake about subdirectories to look into
 # ============================================================================
 
-# ============================================================================
-# Find packages
-# ============================================================================
-find_package(ZLIB REQUIRED)
-
 # ============================================================================
 # libaevol-post is a library that contains classes shared by several
 # post-treatments

test/CMakeLists.txt

 # Google Test headers
 add_subdirectory(googletest)
 
-# We need zlib
-find_package(ZLIB REQUIRED)
-
 # Libraries to link unit tests against
 set(test_libs
   aevol