Temporary header file '/tmp/6fTrjtrIBa/dump1.h' with the following content will be compiled to create GCC translation unit dump:

  // add defines
  #define __STDC_VERSION__ 201710L
#define _GXX_NULLPTR_T
#define CLUTTER_ENABLE_COMPOSITOR_API 1
#define _REGEX_NELTS(n)
#define _Atomic
#define PACKED
#define getaddrinfo_a(a,b,c,d)

  // add includes
  #include "/usr/include/mrpt/io/include/mrpt/io/CFileGZInputStream.h"
  #include "/usr/include/mrpt/io/include/mrpt/io/CFileGZOutputStream.h"
  #include "/usr/include/mrpt/io/include/mrpt/io/CFileInputStream.h"
  #include "/usr/include/mrpt/io/include/mrpt/io/CFileOutputStream.h"
  #include "/usr/include/mrpt/io/include/mrpt/io/CFileStream.h"
  #include "/usr/include/mrpt/io/include/mrpt/io/CMemoryStream.h"
  #include "/usr/include/mrpt/io/include/mrpt/io/CPipe.h"
  #include "/usr/include/mrpt/io/include/mrpt/io/CStream.h"
  #include "/usr/include/mrpt/io/include/mrpt/io/CTextFileLinesParser.h"
  #include "/usr/include/mrpt/io/include/mrpt/io/csv.h"
  #include "/usr/include/mrpt/io/include/mrpt/io/lazy_load_path.h"
  #include "/usr/include/mrpt/io/include/mrpt/io/open_flags.h"
  #include "/usr/include/mrpt/io/include/mrpt/io/registerAllClasses.h"
  #include "/usr/include/mrpt/io/include/mrpt/io/vector_loadsave.h"
  #include "/usr/include/mrpt/io/include/mrpt/io/zip.h"

  // add namespaces
  namespace mrpt{typedef int tmp_add_type_1;}
  mrpt::tmp_add_type_1 tmp_add_func_1(){return 0;};
  namespace mrpt{namespace internal{typedef int tmp_add_type_2;}}
  mrpt::internal::tmp_add_type_2 tmp_add_func_2(){return 0;};
  namespace mrpt{namespace io{typedef int tmp_add_type_3;}}
  mrpt::io::tmp_add_type_3 tmp_add_func_3(){return 0;};
  namespace mrpt{namespace io{namespace internal{typedef int tmp_add_type_4;}}}
  mrpt::io::internal::tmp_add_type_4 tmp_add_func_4(){return 0;};
  namespace mrpt{namespace io{namespace zip{typedef int tmp_add_type_5;}}}
  mrpt::io::zip::tmp_add_type_5 tmp_add_func_5(){return 0;};
  namespace spimpl{typedef int tmp_add_type_6;}
  spimpl::tmp_add_type_6 tmp_add_func_6(){return 0;};
  namespace spimpl{namespace details{typedef int tmp_add_type_7;}}
  spimpl::details::tmp_add_type_7 tmp_add_func_7(){return 0;};

  // add classes
  _G_fpos64_t* tmp_add_class_0;
  _G_fpos_t* tmp_add_class_1;
  _IO_cookie_io_functions_t* tmp_add_class_2;

The GCC parameters:
  gcc -fdump-lang-raw -fkeep-inline-functions -c -x c++ -fpermissive -w "/tmp/6fTrjtrIBa/dump1.h"  -I/usr/include/mrpt/io/include -I/usr/include/mrpt/core/include

In file included from /tmp/6fTrjtrIBa/dump1.h:21:
/usr/include/mrpt/io/include/mrpt/io/csv.h: In function ‘void mrpt::io::load_csv(const std::string&, MATRIX&)’:
/usr/include/mrpt/io/include/mrpt/io/csv.h:54:13: error: ‘Eigen’ has not been declared
   54 |         M = Eigen::Map<const Eigen::Matrix<
      |             ^~~~~
/usr/include/mrpt/io/include/mrpt/io/csv.h:54:24: error: expected primary-expression before ‘const’
   54 |         M = Eigen::Map<const Eigen::Matrix<
      |                        ^~~~~