Add BUILD_SHARED_LIBS as a configurable option

Update build logic to match and also prevent conflicting options

cmake/HandleGeneralOptions.cmake

@@ -21,12 +21,13 @@ if (NOT MSVC)
 endif()
 
 # Configurable Options
+option(BUILD_SHARED_LIBS                     "Build shared libraries" ON)
 if(GTSAM_UNSTABLE_AVAILABLE)
     option(GTSAM_BUILD_UNSTABLE              "Enable/Disable libgtsam_unstable"          ON)
     option(GTSAM_UNSTABLE_BUILD_PYTHON       "Enable/Disable Python wrapper for libgtsam_unstable" ON)
     option(GTSAM_UNSTABLE_INSTALL_MATLAB_TOOLBOX "Enable/Disable MATLAB wrapper for libgtsam_unstable" OFF)
 endif()
-option(GTSAM_FORCE_SHARED_LIB               "Force gtsam to be a shared library, overriding BUILD_SHARED_LIBS" ON)
+option(GTSAM_FORCE_SHARED_LIB               "Force gtsam to be a shared library, overriding BUILD_SHARED_LIBS" OFF)
 option(GTSAM_FORCE_STATIC_LIB               "Force gtsam to be a static library, overriding BUILD_SHARED_LIBS" OFF)
 option(GTSAM_USE_QUATERNIONS                "Enable/Disable using an internal Quaternion representation for rotations instead of rotation matrices. If enable, Rot3::EXPMAP is enforced by default." OFF)
 option(GTSAM_POSE3_EXPMAP                   "Enable/Disable using Pose3::EXPMAP as the default mode. If disabled, Pose3::FIRST_ORDER will be used." ON)
@@ -46,7 +47,9 @@ option(GTSAM_TANGENT_PREINTEGRATION         "Use new ImuFactor with integration
 option(GTSAM_SLOW_BUT_CORRECT_BETWEENFACTOR "Use the slower but correct version of BetweenFactor" OFF)
 option(GTSAM_SLOW_BUT_CORRECT_EXPMAP        "Use slower but correct expmap for Pose2"  OFF)
 
-if (GTSAM_FORCE_SHARED_LIB)
+if (GTSAM_FORCE_SHARED_LIB AND GTSAM_FORCE_STATIC_LIB)
+    message(FATAL_ERROR "GTSAM_FORCE_SHARED_LIB and GTSAM_FORCE_STATIC_LIB are both true. Please, to unambiguously select the desired library type to use to build GTSAM, set one of GTSAM_FORCE_SHARED_LIB=ON, GTSAM_FORCE_STATIC_LIB=ON, or BUILD_SHARED_LIBS={ON/OFF}")
+elseif (GTSAM_FORCE_SHARED_LIB)
     message(STATUS "GTSAM is a shared library due to GTSAM_FORCE_SHARED_LIB")
     set(GTSAM_LIBRARY_TYPE SHARED CACHE STRING "" FORCE)
     set(GTSAM_SHARED_LIB 1 CACHE BOOL "" FORCE)
@@ -55,10 +58,9 @@ elseif (GTSAM_FORCE_STATIC_LIB)
     set(GTSAM_LIBRARY_TYPE STATIC CACHE STRING "" FORCE)
     set(GTSAM_SHARED_LIB 0 CACHE BOOL "" FORCE)
 elseif (BUILD_SHARED_LIBS)
-    message(STATUS "GTSAM is a shared library due to BUILD_SHARED_LIBS is ON")
     set(GTSAM_LIBRARY_TYPE SHARED CACHE STRING "" FORCE)
     set(GTSAM_SHARED_LIB 1 CACHE BOOL "" FORCE)
-elseif((DEFINED BUILD_SHARED_LIBS) AND (NOT BUILD_SHARED_LIBS))
+elseif(NOT BUILD_SHARED_LIBS)
     message(STATUS "GTSAM is a static library due to BUILD_SHARED_LIBS is OFF")
     set(GTSAM_LIBRARY_TYPE STATIC CACHE STRING "" FORCE)
     set(GTSAM_SHARED_LIB 0 CACHE BOOL "" FORCE)