Clarify autotools helper macro

configure.ac

@@ -1665,8 +1665,11 @@ fi
 
 ## TODO - Probably this should be reworked or moved somewhere else
 
-# First arg has name and value. If first in undef, then non-empty second value is default
-m4_define([SETUP_API_TEST_VAR],
+# If the provided name corresponds to a non-empty variable,
+# create a macro with the given name and value. 
+# If the provided name does not exist, create a macro with the 
+# default value if one was provided, otherwise undefine the macro.
+m4_define([EXPORT_VARIABLE],
   [if test -n "$$1"; then
     AC_SUBST([$1], ["#define $1 $$1"])
    else
@@ -1678,44 +1681,38 @@ m4_define([SETUP_API_TEST_VAR],
    fi]
 )
 
-m4_define([SETUP_IF_UNDEF],
-  [if test -z "$$1"; then
-     AC_SUBST([$1], ["#define $1 $2"])
-   fi]
-)
-
-SETUP_API_TEST_VAR([H5_API_TEST_CONFIG_H], ["1"])
+EXPORT_VARIABLE([H5_API_TEST_CONFIG_H], ["1"])
 
 # TODO: These flags are copied from a CMake equivalent H5_api_test_config.h.in 
 # and I haven't verified that the autotools define them
-SETUP_API_TEST_VAR([H5_API_TEST_HAVE_ASYNC], [])
+EXPORT_VARIABLE([H5_API_TEST_HAVE_ASYNC], [])
 if test -n "$H5_HAVE_PARALLEL"; then 
-  SETUP_API_TEST_VAR([MPIEXEC_EXECUTABLE], [])
-  SETUP_API_TEST_VAR([MPIEXEC], [])
+  EXPORT_VARIABLE([MPIEXEC_EXECUTABLE], [])
+  EXPORT_VARIABLE([MPIEXEC], [])
 
-  SETUP_API_TEST_VAR(MPIEXEC_NUMPROC_FLAG, [])
-  SETUP_API_TEST_VAR(MPIEXEC_PREFLAGS, [])
-  SETUP_API_TEST_VAR(MPIEXEC_POSTFLAGS, [])
+  EXPORT_VARIABLE(MPIEXEC_NUMPROC_FLAG, [])
+  EXPORT_VARIABLE(MPIEXEC_PREFLAGS, [])
+  EXPORT_VARIABLE(MPIEXEC_POSTFLAGS, [])
 
-  SETUP_API_TEST_VAR(MPIEXEC_SERVER_PREFLAGS, [])
-  SETUP_API_TEST_VAR(MPIEXEC_SERVER_POSTFLAGS, [])
-  SETUP_API_TEST_VAR(MPIEXEC_MAX_NUMPROCS, [])
+  EXPORT_VARIABLE(MPIEXEC_SERVER_PREFLAGS, [])
+  EXPORT_VARIABLE(MPIEXEC_SERVER_POSTFLAGS, [])
+  EXPORT_VARIABLE(MPIEXEC_MAX_NUMPROCS, [])
 fi
 
-SETUP_API_TEST_VAR([DART_TESTING_TIMEOUT], ["1500"])
+EXPORT_VARIABLE([DART_TESTING_TIMEOUT], ["1500"])
 
 
-SETUP_API_TEST_VAR([H5_API_TEST_ENV_VARS], [])
-SETUP_API_TEST_VAR([H5_API_TEST_INIT_COMMAND], [])
+EXPORT_VARIABLE([H5_API_TEST_ENV_VARS], [])
+EXPORT_VARIABLE([H5_API_TEST_INIT_COMMAND], [])
 
-SETUP_API_TEST_VAR([H5_API_TEST_SERVER_START_MSG], [])
-SETUP_API_TEST_VAR([H5_API_TEST_SERVER_EXIT_COMMAND], [])
+EXPORT_VARIABLE([H5_API_TEST_SERVER_START_MSG], [])
+EXPORT_VARIABLE([H5_API_TEST_SERVER_EXIT_COMMAND], [])
 
-SETUP_API_TEST_VAR([H5_API_TEST_CLIENT_HELPER_START_MSG], [])
-SETUP_API_TEST_VAR([H5_API_TEST_CLIENT_HELPER_EXIT_COMMAND], [])
+EXPORT_VARIABLE([H5_API_TEST_CLIENT_HELPER_START_MSG], [])
+EXPORT_VARIABLE([H5_API_TEST_CLIENT_HELPER_EXIT_COMMAND], [])
 
-SETUP_API_TEST_VAR([H5_API_TEST_CLIENT_INIT_TOKEN_REGEX], [])
-SETUP_API_TEST_VAR([H5_API_TEST_CLIENT_INIT_TOKEN_VAR], [])
+EXPORT_VARIABLE([H5_API_TEST_CLIENT_INIT_TOKEN_REGEX], [])
+EXPORT_VARIABLE([H5_API_TEST_CLIENT_INIT_TOKEN_VAR], [])