Workaround for PGI bug with variable length string pointer

PGI has problems with elpa_int_value_to_string() where we return a
variable-length string pointer. A workaround for now is to copy the string into
a non-pointer variable of the same length.

This closes issue #55

configure.ac

@@ -958,10 +958,18 @@ m4_include([m4/ax_fc_check_define.m4])
 AC_MSG_CHECKING([if workaround for broken preprocessor is needed])
 
 need_manual_cpp=no
-AX_FC_CHECK_DEFINE([__INTEL_COMPILER],[need_manual_cpp=yes],[])
-AX_FC_CHECK_DEFINE([__PGI],[need_manual_cpp=yes],[])
+AX_FC_CHECK_DEFINE([__INTEL_COMPILER],[is_intel=yes],[])
+AX_FC_CHECK_DEFINE([__PGI],[is_pgi=yes],[])
 ACTUAL_FC="$FC"
 AC_SUBST([ACTUAL_FC])
+
+if test x"$is_intel" = x"yes" ; then
+	need_manual_cpp=yes
+fi
+if test x"$is_pgi" = x"yes" ; then
+	need_manual_cpp=yes
+fi
+
 if test x"$need_manual_cpp" = x"yes" ; then
         AC_MSG_RESULT([yes])
         FC="\$(top_srcdir)/manual_cpp $FC"
@@ -969,6 +977,10 @@ else
         AC_MSG_RESULT([no])
 fi
 
+if test x"$is_pgi" = x"yes" ; then
+	AC_DEFINE([PGI_VARIABLE_STRING_BUG], [1], [Work around a PGI bug with variable-length string results])
+fi
+
 
 dnl PGI compiler uses -module to specify module output
 dnl directory. This clashes with libtools -module link option

src/elpa_api.F90

@@ -1207,15 +1207,31 @@ module elpa_api
       character(kind=c_char, len=*), intent(in) :: name
       integer(kind=c_int), intent(in) :: value
       integer(kind=c_int), intent(out), optional :: error
+
+#ifdef PGI_VARIABLE_STRING_BUG
+      character(kind=c_char, len=elpa_int_value_to_strlen_c(name // C_NULL_CHAR, value)), pointer :: string_ptr
+      character(kind=c_char, len=elpa_int_value_to_strlen_c(name // C_NULL_CHAR, value)) :: string
+#else
       character(kind=c_char, len=elpa_int_value_to_strlen_c(name // C_NULL_CHAR, value)), pointer :: string
+#endif
+
       integer(kind=c_int) :: actual_error
       type(c_ptr) :: ptr
 
       actual_error = elpa_int_value_to_string_c(name // C_NULL_CHAR, value, ptr)
       if (c_associated(ptr)) then
+#ifdef PGI_VARIABLE_STRING_BUG
+        call c_f_pointer(ptr, string_ptr)
+        string = string_ptr
+#else
         call c_f_pointer(ptr, string)
+#endif
       else
+#ifdef PGI_VARIABLE_STRING_BUG
+        nullify(string_ptr)
+#else
         nullify(string)
+#endif
       endif
 
       if (present(error)) then