When test-compiling to check for jit, also use CFLAGS and LIBS

rather than the values from pkg-config only. CLAGS and LIBS
may contain important generic compiler / linker flags for this
platform.

configure.ac

@@ -160,9 +160,9 @@ AC_ARG_ENABLE(pcre-jit,
 if test "$enable_pcre_jit" = yes; then
   AC_MSG_CHECKING(for PCRE JIT usability)
   save_CFLAGS="${CFLAGS}"
-  CFLAGS="${PCRE_CFLAGS}"
+  CFLAGS="${CFLAGS} ${PCRE_CFLAGS}"
   save_LIBS="${LIBS}"
-  LIBS="${PCRE_LIBS}"
+  LIBS="${LIBS} ${PCRE_LIBS}"
   AC_RUN_IFELSE(
     [AC_LANG_PROGRAM([[
 #include <pcre.h>