oset-c++: Avoid compilation error with nvc++ 22.1

[Bruno Haible]

With the nvc and nvc++ compilers, I get this compilation error:

nvc++ -DHAVE_CONFIG_H -DEXEEXT=\"\" -I. -I../../gltests -I..  
-DGNULIB_STRICT_CHECKING=1 -DIN_GNULIB_TESTS=1 -I. -I../../gltests -I.. 
-I../../gltests/.. -I../gllib -I../../gltests/../gllib 
-I/home/bruno/prefix-nvc/include -Wall  -g -O2 -c -o test-oset-c++.o 
../../gltests/test-oset-c++.cc
"../../gltests/../gllib/gl_oset.hh", line 160: warning: class template 
"gl_OSet<ELTYPE *>" has no member "begin"
      friend iterator gl_OSet::begin ();
                               ^

"../../gltests/../gllib/gl_oset.hh", line 162: error: declaration is 
incompatible with function template "gl_OSet<const char *>::iterator 
gl_OSet<ELTYPE *>::begin_atleast(bool (*)(const char *, THT *), THT *) [with 
ELTYPE=const char]" (declared at line 193)
      friend iterator gl_OSet::begin_atleast (bool (*) (ELTYPE *, THT *), THT 
*);
                               ^
          detected during instantiation of class "gl_OSet<ELTYPE *>::iterator 
[with ELTYPE=const char]" at line 60 of "../../gltests/test-oset-c++.cc"

"../../gltests/../gllib/gl_oset.hh", line 195: error: "gl_OSet<ELTYPE 
*>::iterator::iterator(gl_oset_t, bool (*)(ELTYPE *, THT *), THT *) [with 
ELTYPE=const char, THT=const char]" (declared at line 170) is inaccessible
      { return iterator (_ptr, threshold_fn, threshold); }
               ^
          detected during instantiation of "gl_OSet<ELTYPE *>::iterator 
gl_OSet<ELTYPE *>::begin_atleast(bool (*)(ELTYPE *, THT *), THT *) [with 
ELTYPE=const char, THT=const char]" at line 87 of 
"../../gltests/test-oset-c++.cc"

2 errors detected in the compilation of "../../gltests/test-oset-c++.cc".


This patch fixes it.
Note that the compiler defines both __EDG__ and __PGIC__. The former apparently
describes the C++ frontend, the latter the code generation phase.


2022-01-15  Bruno Haible  <bruno@clisp.org>

        oset-c++: Avoid compilation error with nvc++ 22.1.
        * lib/gl_oset.hh: With EDG C++ compilers, avoid 'friend'.

diff --git a/lib/gl_oset.hh b/lib/gl_oset.hh
index d1bb4893f6..4fae4eb4d6 100644
--- a/lib/gl_oset.hh
+++ b/lib/gl_oset.hh
@@ -153,7 +153,7 @@ public:
     ~iterator ()
       { gl_oset_iterator_free (&_state); }
 
-  #if defined __xlC__ || defined __HP_aCC || defined __SUNPRO_CC
+  #if defined __xlC__ || defined __HP_aCC || defined __SUNPRO_CC || defined 
__EDG__
   public:
   #else
   private: