Fixed conditional compilation issues

And added a comment

src/algorithms/signal_source/libs/ion_gsms_stream_encodings.h

@@ -3,6 +3,8 @@
  * \brief Implements look up tables for all encodings in the standard
  * \author Víctor Castillo Agüero, 2024. victorcastilloaguero(at)gmail.com
  *
+ * These tables are taken from the stardard's official document.
+ *
  * -----------------------------------------------------------------------------
  *
  * GNSS-SDR is a Global Navigation Satellite System software-defined receiver.

src/core/receiver/CMakeLists.txt

@@ -70,6 +70,10 @@ if(ENABLE_FPGA)
     target_compile_definitions(core_receiver PUBLIC -DENABLE_FPGA=1)
 endif()
 
+if(ENABLE_ION)
+    target_compile_definitions(core_receiver PRIVATE -DENABLE_ION_SOURCE=1)
+endif()
+
 if(GNURADIO_USES_STD_POINTERS)
     target_compile_definitions(core_receiver PUBLIC -DGNURADIO_USES_STD_POINTERS=1)
 endif()

src/core/receiver/gnss_block_factory.cc

@@ -93,7 +93,6 @@
 #include "ibyte_to_complex.h"
 #include "ibyte_to_cshort.h"
 #include "in_memory_configuration.h"
-#include "ion_gsms_signal_source.h"
 #include "ishort_to_complex.h"
 #include "ishort_to_cshort.h"
 #include "labsat_signal_source.h"
@@ -197,6 +196,10 @@
 #include "gps_l1_ca_dll_pll_tracking_gpu.h"
 #endif
 
+#if ENABLE_ION_SOURCE
+#include "ion_gsms_signal_source.h"
+#endif
+
 using namespace std::string_literals;
 
 namespace
@@ -760,13 +763,14 @@ std::unique_ptr<GNSSBlockInterface> GNSSBlockFactory::GetBlock(
                     block = std::move(block_);
                 }
 #endif
+#if ENABLE_ION_SOURCE
             else if (implementation == "ION_GSMS_Signal_Source")
                 {
                     std::unique_ptr<GNSSBlockInterface> block_ = std::make_unique<IONGSMSSignalSource>(configuration, role, in_streams,
                         out_streams, queue);
                     block = std::move(block_);
                 }
-
+#endif
 #if RAW_ARRAY_DRIVER
             else if (implementation == "Raw_Array_Signal_Source")
                 {