Not sure whether anyone cares about supporting ancient Linux versions...
But RHEL 5.x shipped with librsvg2 2.16.1, which did not provide the
LIBSRVG_CHECK_VERSION macro.

Simple patch below allows Emacs 26.3 to compile on RHEL/CentOS 5.

 - Pat

diff -u -r emacs-26.3-orig/src/image.c emacs-26.3/src/image.c
--- emacs-26.3-orig/src/image.c 2019-06-12 03:50:42.000000000 -0700
+++ emacs-26.3/src/image.c      2019-08-29 10:13:13.000000000 -0700
@@ -9313,9 +9313,11 @@
   #if GNUC_PREREQ (4, 6, 0)
    #pragma GCC diagnostic push
   #endif
+  #if defined(LIBSRVG_CHECK_VERSION)
   #if LIBRSVG_CHECK_VERSION (2, 45, 1) && GNUC_PREREQ (4, 2, 0)
    #pragma GCC diagnostic ignored "-Wdeprecated-declarations"
   #endif
+  #endif

   /* Parse the contents argument and fill in the rsvg_handle.  */
   rsvg_handle_write (rsvg_handle, (unsigned char *) contents, size, &err);