cmake: add an option for building with PIC

When building statically, PIC may still be wanted in order to be used in
a shared library elsewhere.

CMakeLists.txt

@@ -454,6 +454,10 @@ ELSE()
   SET(KWSYS_LIBRARY_TYPE STATIC)
 ENDIF()
 
+if(NOT DEFINED KWSYS_BUILD_PIC)
+  set(KWSYS_BUILD_PIC 0)
+endif()
+
 #-----------------------------------------------------------------------------
 # Configure some implementation details.
 
@@ -870,7 +874,7 @@ IF(KWSYS_C_SRCS OR KWSYS_CXX_SRCS)
     SET(KWSYS_LINK_DEPENDENCY INTERFACE)
     ADD_LIBRARY(${KWSYS_TARGET_OBJECT} OBJECT
       ${KWSYS_C_SRCS} ${KWSYS_CXX_SRCS})
-    IF(KWSYS_BUILD_SHARED)
+    IF(KWSYS_BUILD_SHARED OR KWSYS_BUILD_PIC)
       SET_PROPERTY(TARGET ${KWSYS_TARGET_OBJECT} PROPERTY
         POSITION_INDEPENDENT_CODE TRUE)
     ENDIF()
@@ -965,7 +969,7 @@ IF(KWSYS_ENABLE_C AND KWSYS_C_SRCS)
       ${KWSYS_TARGET_C_INTERFACE} ${KWSYS_TARGET_C_LINK})
     SET(KWSYS_LINK_DEPENDENCY INTERFACE)
     ADD_LIBRARY(${KWSYS_TARGET_C_OBJECT} OBJECT ${KWSYS_C_SRCS})
-    IF(KWSYS_BUILD_SHARED)
+    IF(KWSYS_BUILD_SHARED OR KWSYS_BUILD_PIC)
       SET_PROPERTY(TARGET ${KWSYS_TARGET_C_OBJECT} PROPERTY
         POSITION_INDEPENDENT_CODE TRUE)
     ENDIF()