[libxslt] Compile with -Wextra

[Nick Wellnhofer <nwellnhof src gnome org>]

commit e85f12dffee6eb1fc98864afa16b87376e175429
Author: Nick Wellnhofer <wellnhofer aevum de>
Date:   Sat May 11 14:30:03 2019 +0200

    Compile with -Wextra
    
    Also run Travis tests with -Werror.

 .travis.yml         | 4 ++--
 configure.ac        | 2 +-
 libxslt/variables.c | 8 +++++---
 3 files changed, 8 insertions(+), 6 deletions(-)
---
diff --git a/.travis.yml b/.travis.yml
index 172d1e2f..f1e589eb 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -7,12 +7,12 @@ matrix:
     # TODO: Build and test Python bindings.
     - compiler: gcc
       env: CONFIG="--without-python"
-           CFLAGS="-O2 -std=c89 -D_POSIX_C_SOURCE=200112L"
+           CFLAGS="-O2 -std=c89 -D_POSIX_C_SOURCE=200112L -Werror -Wno-error=array-bounds"
     # clang with AddressSanitizer and UndefinedBehaviorSanitizer.
     - compiler: clang
       dist: trusty
       env: CONFIG="--without-python"
-           CFLAGS="-O2 -g -fno-omit-frame-pointer -fsanitize=address,undefined -fno-sanitize-recover=all"
+           CFLAGS="-O2 -g -fno-omit-frame-pointer -fsanitize=address,undefined -fno-sanitize-recover=all 
-Werror -Wno-error=cast-align"
            UBSAN_OPTIONS=print_stacktrace=1
 script:
 - |
diff --git a/configure.ac b/configure.ac
index f932049c..501bb391 100644
--- a/configure.ac
+++ b/configure.ac
@@ -474,7 +474,7 @@ if test "${GCC}" != "yes" ; then
                ;;
     esac
 else
-    CFLAGS="${CFLAGS} -Wall -Wformat=2 -Wmissing-format-attribute"
+    CFLAGS="${CFLAGS} -Wall -Wextra -Wformat=2 -Wmissing-format-attribute"
     case "${host}" in
           alpha*-*-linux* )
               CFLAGS="${CFLAGS} -mieee"
diff --git a/libxslt/variables.c b/libxslt/variables.c
index 8f88e573..2982f092 100644
--- a/libxslt/variables.c
+++ b/libxslt/variables.c
@@ -205,7 +205,8 @@ xsltRegisterLocalRVT(xsltTransformContextPtr ctxt,
  * This function is unsupported in newer releases of libxslt.
  */
 int
-xsltExtensionInstructionResultFinalize(xsltTransformContextPtr ctxt)
+xsltExtensionInstructionResultFinalize(
+        xsltTransformContextPtr ctxt ATTRIBUTE_UNUSED)
 {
     xmlGenericError(xmlGenericErrorContext,
             "xsltExtensionInstructionResultFinalize is unsupported "
@@ -230,8 +231,9 @@ xsltExtensionInstructionResultFinalize(xsltTransformContextPtr ctxt)
  * libxslt.
  */
 int
-xsltExtensionInstructionResultRegister(xsltTransformContextPtr ctxt,
-                                      xmlXPathObjectPtr obj)
+xsltExtensionInstructionResultRegister(
+        xsltTransformContextPtr ctxt ATTRIBUTE_UNUSED,
+       xmlXPathObjectPtr obj ATTRIBUTE_UNUSED)
 {
     return(0);
 }