Make test_exported_symbols stricter.

* Do not allow for the leading underscores of the xt_* symbols
  when they are not expected and enforce them otherwise.
* Also add special rules for compilers previously covered by the
  broader rule.
* And move variable substitution to top of script.

Co-authored-by: Thomas Jahns <jahns@dkrz.de>

configure.ac

@@ -114,7 +114,7 @@ AM_PROG_CC_C_O
 # Set up libtool.
 ACX_USE_LIBTOOL_CONFIGURATION
 AC_SUBST([lt_cv_nm_interface])
-acx_symprfx=$ac_symprfx
+AC_SUBST([acx_symprfx],[$ac_symprfx])
 dnl ######################################################################
 dnl Properties of the compiler
 dnl ######################################################################

tests/test_exported_symbols.in

@@ -49,6 +49,7 @@ NM="@NM@"
 lt_cv_nm_interface="@lt_cv_nm_interface@"
 abs_builddir="@abs_builddir@"
 abs_top_builddir="@abs_top_builddir@"
+acx_symprfx="@acx_symprfx@"
 if [ x"$lt_cv_nm_interface" = x"BSD nm" ]; then
   exp_sym_prefix='[0-9a-fA-F]*[ 	][ 	]*[TDBGRSVW][ 	]'
   badsyms=$("$abs_top_builddir"/libtool --mode=clean --silent \
@@ -77,12 +78,15 @@ if [ x"$lt_cv_nm_interface" = x"BSD nm" ]; then
 /^${exp_sym_prefix}\(__NAGf90_\|f90_\)/b
 # ignore symbols pgfortran/pgcc injects into our shared objects
 /^${exp_sym_prefix}\(__get_xmmreg\|__pgdbg_stub\|__pgi_trace\|__set_xmmreg\|__pgi_data_section_start\|_mp_preinit\)/b
-# skip symbols that conform to name prefix xt_
-/^${exp_sym_prefix}_*[Xx][Tt]_/b
+# skip symbols that conform to name prefix xt_ or Fortran yaxt module
+# ifort adds a symbol 'yaxt._'
+/^${exp_sym_prefix}${acx_symprfx}\\([Yy][Aa]\\)\\{0,1\\}[Xx][Tt]\\.\\{0,1\\}_/b
+# gfortran module member names start with module name prefixed by two underscores
+/^${exp_sym_prefix}__yaxt_MOD_/b
 # also skip symbols mangled by asan
 /^[0-9a-fA-F]*[ 	][ 	]*B[ 	]__odr_asan\\.[Xx][Tt]\.*/b
-# also skip symbols in Fortran yaxt module
-/^${exp_sym_prefix}_*[Yy][Aa][Xx][Tt]\.*_/b
+# PGI compiler prefixes D and B entries of modules with underscore
+/^[0-9a-fA-F]*[ 	][ 	]*[DB][ 	]_\\([Yy][Aa]\\)\\{0,1\\}[Xx][Tt]_/b
 # skip $-symbols that the Cray compiler puts in
 /^${exp_sym_prefix}.*\\\$.*/b
 # skip internal symbols for stubs created by xlf