Makefile.am: also compile yacc/bison files with special warnings

Just as for flex, the yacc/bison files produce code that generates
warnings during the build. These warnings show up when compiling
with clang version 18 or later. Since we can't change the code
produced by these tools, we need to disable some compile warnings
for these files.

Makefile.am

@@ -1825,16 +1825,17 @@ endif
 # sources only.
 sieve_libcyrus_sieve_lex_la_SOURCES = \
     sieve/addr-lex.l \
-    sieve/sieve-lex.l
+    sieve/sieve-lex.l \
+    sieve/addr.y \
+    sieve/sieve.y
 sieve_libcyrus_sieve_lex_la_LIBADD =
-sieve_libcyrus_sieve_lex_la_CFLAGS = $(AM_CFLAGS) $(CFLAG_VISIBILITY) $(NOWARN_SIGN_COMPARE)
+sieve_libcyrus_sieve_lex_la_CFLAGS = $(AM_CFLAGS) $(CFLAG_VISIBILITY) $(NOWARN_SIGN_COMPARE) $(NOWARN_UNUSED_BUT_SET)
 
 nodist_sieve_libcyrus_sieve_la_SOURCES = \
     sieve/sieve_err.c \
     sieve/sieve_err.h
 sieve_libcyrus_sieve_la_SOURCES = \
     sieve/bytecode.h \
-    sieve/addr.y \
     sieve/bc_emit.c \
     sieve/bc_eval.c \
     sieve/bc_generate.c \
@@ -1852,7 +1853,6 @@ sieve_libcyrus_sieve_la_SOURCES = \
     sieve/message.h \
     sieve/script.c \
     sieve/script.h \
-    sieve/sieve.y \
     sieve/tree.c \
     sieve/tree.h \
     sieve/variables.c \

configure.ac

@@ -873,6 +873,21 @@ AC_COMPILE_IFELSE(
 CFLAGS="$saved_CFLAGS"
 AC_SUBST([NOWARN_SIGN_COMPARE])
 
+dnl look for an option to disable sign-comparison warnings (needed for
+dnl flex-generated sieve sources when building with -Werror)
+saved_CFLAGS="$CFLAGS"
+NOWARN_UNUSED_BUT_SET="-Wno-unused-but-set-variable"
+CFLAGS="$NOWARN_UNUSED_BUT_SET"
+AC_MSG_CHECKING([whether the C compiler supports -Wno-unused-but-set-variable])
+AC_COMPILE_IFELSE(
+    [AC_LANG_PROGRAM([], [])],
+    [AC_MSG_RESULT([yes])],
+    [NOWARN_UNUSED_BUT_SET=]
+    [AC_MSG_RESULT([no])]
+)
+CFLAGS="$saved_CFLAGS"
+AC_SUBST([NOWARN_UNUSED_BUT_SET])
+
 dnl for et routines
 AC_FUNC_CHECK(strerror,AC_DEFINE(HAS_STRERROR,[],[Do we have strerror()?]),
               AC_DEFINE(NEED_SYS_ERRLIST,[],[Do we have a sys_errlist?]))