[build] Hush the Solaris compiler about enum abuse.

Sun Studio 12 doesn't like it when we mix our
enum values and types.  We do that a lot on purpose
so the warnings from compiles were very verbose.

build/aclocal.cairo.m4

@@ -111,21 +111,40 @@ AC_DEFUN([CAIRO_CC_TRY_FLAG_SILENT],
 	fi
 ])
 
+dnl find a -Werror equivalent
+AC_DEFUN([CAIRO_CC_CHECK_WERROR],
+[dnl
+	_test_WERROR=${WERROR+set}
+	if test "z$_test_WERROR" != zset; then
+		WERROR=""
+		for _werror in -Werror -errwarn; do
+			AC_MSG_CHECKING([whether $CC supports $_werror])
+			CAIRO_CC_TRY_FLAG_SILENT(
+				[$_werror],,
+				[WERROR="$WERROR $_werror"],
+				[:])
+			AC_MSG_RESULT($cairo_cc_flag)
+		done
+	fi
+])
+
 dnl check compiler flags possibly using -Werror if available.
 AC_DEFUN([CAIRO_CC_TRY_FLAG],
 [dnl     (flags..., optional program, true-action, false-action)
+	CAIRO_CC_CHECK_WERROR
 	AC_MSG_CHECKING([whether $CC supports $1])
-	CAIRO_CC_TRY_FLAG_SILENT([-Werror $1], [$2], [$3], [$4])
+	CAIRO_CC_TRY_FLAG_SILENT([$WERROR $1], [$2], [$3], [$4])
 	AC_MSG_RESULT([$cairo_cc_flag])
 ])
 
 dnl check compiler/ld flags
 AC_DEFUN([CAIRO_CC_TRY_LINK_FLAG],
 [dnl
+	CAIRO_CC_CHECK_WERROR
 	AC_MSG_CHECKING([whether $CC supports $1])
 
 	_save_cflags="$CFLAGS"
-	CFLAGS="$CFLAGS -Werror $1"
+	CFLAGS="$CFLAGS $WERROR $1"
 	AC_LINK_IFELSE([int main(void){ return 0;} ],
                        [cairo_cc_flag=yes],
                        [cairo_cc_flag=no])

build/configure.ac.warnings

@@ -19,6 +19,12 @@ MAYBE_WARN="-Wall -Wextra \
 -Wno-missing-field-initializers -Wno-unused-parameter \
 -Wno-attributes -Wno-long-long -Winline"
 
+dnl Sun Studio 12 likes to rag at us for abusing enums like
+dnl having cairo_status_t variables hold cairo_int_status_t
+dnl values.  It's bad, we know.  Now please be quiet.
+MAYBE_WARN="$MAYBE_WARN -erroff=E_ENUM_TYPE_MISMATCH_ARG \
+			-erroff=E_ENUM_TYPE_MISMATCH_OP"
+
 dnl We also abuse the warning-flag facility to enable other compiler
 dnl options.  Namely, the following:
 MAYBE_WARN="$MAYBE_WARN -fno-strict-aliasing -fno-common"