obstack, libc-config: Support HP-UX cc in C99 mode

[Bruno Haible]

Testing a 'grep' snapshot on HP-UX 11.31 hppa, in 32-bit mode,
with cc (as I don't have a gcc on that machine), more precisely
CC="cc -AC99 -D_XOPEN_SOURCE=500", I get this compilation error:

  CC       obstack.o
cc: "../../lib/obstack.h", line 175: error 1687: Illegal use of flexible array: 
structs with FAMs cannot be members of other structs. 
cc: "../../lib/obstack.c", line 139: warning 521: Incompatible pointer types.
cc: "../../lib/obstack.c", line 204: warning 604: Pointers are not 
assignment-compatible.
cc: "../../lib/obstack.c", line 209: warning 521: Incompatible pointer types.
cc: "../../lib/obstack.c", line 219: warning 521: Incompatible pointer types.
cc: "../../lib/obstack.c", line 252: warning 604: Pointers are not 
assignment-compatible.
cc: "../../lib/obstack.c", line 273: warning 604: Pointers are not 
assignment-compatible.
cc: "../../lib/obstack.c", line 297: warning 604: Pointers are not 
assignment-compatible.
gmake[2]: *** [obstack.o] Error 1

The reason is that __STDC_VERSION__ expands to 199901L; however, the
compiler apparently has bugs regarding flexible-array-members.

This is a regression from 2016-11-15.

This patch fixes it (and other occurrences of the same idiom in other files
as well):


2018-12-16  Bruno Haible  <address@hidden>

        obstack, libc-config: Support HP-UX cc in C99 mode.
        * lib/obstack.h (__FLEXIBLE_ARRAY_MEMBER): Treat HP-UX cc as a pre-C99
        compiler, even when in C99 mode.
        * lib/cdefs.h (__flexarr): Likewise.
        * lib/gettext.h (_LIBGETTEXT_HAVE_VARIABLE_SIZE_ARRAYS): Update comment.

diff --git a/lib/obstack.h b/lib/obstack.h
index ed95cce..4a89331 100644
--- a/lib/obstack.h
+++ b/lib/obstack.h
@@ -111,7 +111,7 @@
 #include <stddef.h>             /* For size_t and ptrdiff_t.  */
 #include <string.h>             /* For __GNU_LIBRARY__, and memcpy.  */
 
-#if __STDC_VERSION__ < 199901L
+#if __STDC_VERSION__ < 199901L || defined __HP_cc
 # define __FLEXIBLE_ARRAY_MEMBER 1
 #else
 # define __FLEXIBLE_ARRAY_MEMBER
diff --git a/lib/cdefs.h b/lib/cdefs.h
index 98cf749..26e2f3f 100644
--- a/lib/cdefs.h
+++ b/lib/cdefs.h
@@ -139,7 +139,7 @@
    Headers that should use flexible arrays only if they're "real"
    (e.g. only if they won't affect sizeof()) should test
    #if __glibc_c99_flexarr_available.  */
-#if defined __STDC_VERSION__ && __STDC_VERSION__ >= 199901L
+#if defined __STDC_VERSION__ && __STDC_VERSION__ >= 199901L && !defined __HP_cc
 # define __flexarr     []
 # define __glibc_c99_flexarr_available 1
 #elif __GNUC_PREREQ (2,97)
diff --git a/lib/gettext.h b/lib/gettext.h
index 27c754c..d5d56ec 100644
--- a/lib/gettext.h
+++ b/lib/gettext.h
@@ -185,7 +185,7 @@ npgettext_aux (const char *domain,
 #include <string.h>
 
 #if (((__GNUC__ >= 3 || __GNUG__ >= 2) && !defined __STRICT_ANSI__) \
-     /* || __STDC_VERSION__ == 199901L
+     /* || (__STDC_VERSION__ == 199901L && !defined __HP_cc)
         || (__STDC_VERSION__ >= 201112L && !defined __STDC_NO_VLA__) */ )
 # define _LIBGETTEXT_HAVE_VARIABLE_SIZE_ARRAYS 1
 #else