Enforces that either static or dynamic libs are built

--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -542,7 +542,7 @@ option(CGNS_USE_SHARED "Link programs to the CGNS shared library" "ON")
 if (CGNS_ENABLE_FORTRAN)
     add_library(cgns_static STATIC ${cgns_FILES} $<TARGET_OBJECTS:cgns_f2c>)
 else (CGNS_ENABLE_FORTRAN)
-  add_library(cgns_static STATIC ${cgns_FILES})
+  add_library(cgns_static STATIC EXCLUDE_FROM_ALL ${cgns_FILES})
 endif (CGNS_ENABLE_FORTRAN)
 # Needed to work around a CMake > 3.8 bug on Windows with MSVS and Intel Fortran
 set_property(TARGET cgns_static PROPERTY LINKER_LANGUAGE C)
@@ -598,7 +598,9 @@ if(CGNS_BUILD_SHARED)
 endif(CGNS_BUILD_SHARED)
 
 # Set the install path of the static library
+if(NOT CGNS_BUILD_SHARED)
 install(TARGETS cgns_static ARCHIVE DESTINATION lib)
+endif()
 # Set the install path of the shared library
 if(CGNS_BUILD_SHARED)
   # for windows, need to install both cgnsdll.dll and cgnsdll.lib
@@ -650,7 +652,6 @@ install(FILES ${headers}
 # Tools #
 #########
 
-add_subdirectory(tools)
 
 #########
 # Tests #