docs/developers.txt: update about C89/GNU89 support (with GCC toolkit)

docs/developers.txt

@@ -134,7 +134,7 @@ miserably for anyone on an older system.  That means you must not use
 it.  gcc only warns about this with -pedantic.
 
 Another feature that does not work on some compilers (e.g. conforming
-to ANSI C / C89 standard) is initial variable declaration inside a
+to "ANSI C"/C89/C90 standard) is initial variable declaration inside a
 'for loop' block, like this:
 --------------------------------------------------------------------------------
 function do_stuff(void)
@@ -152,17 +152,24 @@ C99 (or rather GNU99 on many systems) or newer standard.
 
 The NUT codebase may build in a mode without warnings made fatal on C89
 (GNU89), but the emitted warnings indicate that those binaries may crash.
+By the end of 2021, NUT codebase has been revised to pass GNU and strict-C
+mode builds with C89 standard with the GCC toolkit (and on systems that do
+have the newer features in libraries, just hide them in standard headers);
+however CLANG toolkit is more restrictive about the C99+ syntax used.
 If somebody in the community requires to build and run NUT on systems
 that old, pull requests to fix the offending coding issues are welcome.
 
 Note also that the NUT codebase currently relies on certain features,
-such as the printf format modifiers for `(s)size_t`, that a pedantic C90
-mode compilation warns is not part of the standard but a GNU extension
-(and part of C99 and newer standard revisions).
+such as the printf format modifiers for `(s)size_t`, use of `long long`,
+some nuances about structure/array initializers, variadic macros for
+debugging, etc. that a pedantic C90 mode compilation warns is not part
+of the standard but a GNU extension (and part of C99 and newer standard
+revisions). Many of the "offences" against the older standard actually
+come from system and third-party header files.
 
 That said, the NUT CI farm does run non-regression builds with GNU C89
-standard revision and minimal warnings level, to ensure that codebase
-remains at least basically compliant.
+and strict C89 standard revisions and minimal passing warnings level,
+to ensure that codebase is and remains at least basically compliant.
 
 Continuous Integration and Automated Builds
 -------------------------------------------

docs/nut.dict

@@ -1,4 +1,4 @@
-personal_ws-1.1 en 2801 utf-8
+personal_ws-1.1 en 2804 utf-8
 AAS
 ACFAIL
 ACFREQ
@@ -1854,6 +1854,8 @@ inh
 init
 init's
 initctl
+initializer
+initializers
 initinfo
 initscripts
 initups
@@ -2725,6 +2727,7 @@ var's
 varargs
 varhigh
 variable's
+variadic
 varlow
 varname
 varvalue