make sure that the config.h is accessible for the PMusr lib.

src/classes/CMakeLists.txt

@@ -138,6 +138,7 @@ target_include_directories(
     $<BUILD_INTERFACE:${CMAKE_SOURCE_DIR}/src/external/MuSR_software/Class_MuSR_PSI>
     $<BUILD_INTERFACE:${CMAKE_SOURCE_DIR}/src/external/mud/src>
     $<BUILD_INTERFACE:${CMAKE_SOURCE_DIR}/src/external/nexus>
+    $<BUILD_INTERFACE:${CMAKE_BINARY_DIR}>
 )
 
 add_library(PUserFcnBase SHARED
@@ -151,6 +152,7 @@ add_library(PRgeHandler SHARED
 )
 
 #--- set target properties, e.g. version --------------------------------------
+target_compile_options(PMusr BEFORE PRIVATE "-DHAVE_CONFIG_H")
 set_target_properties(PMusr
   PROPERTIES
     VERSION ${MUSR_VERSION}