Trying the patch you suggested results in same fail for me.

./../../libcdio-2.1.0/lib/driver/_cdio_generic.c:63:20: error: implicit declaration of function 'lseek64'; did you mean 'lseek'? [-Wimplicit-function-declaration]
   63 | #define CDIO_LSEEK lseek64
      |                    ^~~~~~~
../../../libcdio-2.1.0/lib/driver/_cdio_generic.c:173:10: note: in expansion of macro 'CDIO_LSEEK'
  173 |   return CDIO_LSEEK(p_env->fd, offset, whence);
      |          ^~~~~~~~~~
../../../libcdio-2.1.0/lib/driver/_cdio_generic.c:63:20: warning: nested extern declaration of 'lseek64' [-Wnested-externs]
   63 | #define CDIO_LSEEK lseek64
      |                    ^~~~~~~
../../../libcdio-2.1.0/lib/driver/_cdio_generic.c:173:10: note: in expansion of macro 'CDIO_LSEEK'
  173 |   return CDIO_LSEEK(p_env->fd, offset, whence);
      |          ^~~~~~~~~~
make[3]: * [Makefile:778: _cdio_generic.lo] Error 1

Not sure why it failed but I have confirmed the patched applied successfully.

(file #56174)

Based on the Gentoo build log https://918988.bugs.gentoo.org/attachment.cgi?id=876262

It looks like the configure test for fseeko64 succeeds, when we go to compile it there are different GCC flags used, namely
-Wimplicit-function-declaration and warning is treated as an error.

A simple fix is either to omit  -Wimplicit-function-declaration as a compile flag or add it to the flags used in checking for functions:

diff --git a/configure.ac b/configure.ac
index 0399a718..610948a9 100644
--- a/configure.ac
+++ b/configure.ac
@@ -117,6 +117,7 @@ else
         -Wdeclaration-after-statement
         -Wdisabled-optimization
         -Wendif-labels
+        -Wimplicit-function-declaration
         -Winline
         -Wmissing-declarations
         -Wmissing-prototypes

It looks to me as though the essential change is to replace CDIO_LSEEK with lseek unconditionally. CDIO_LSEEK is macro that can be lseek64 or lseek depending on a configure feature check. This check is removed in this patch.

So when you run configure, does configure indicate that fseeko64 exists but when you go to use it it says it is not defined?

I'd appreciate more detail here. You give a build log which shows configure output when the patch is applied, but how about without it applied?

<heitbaum> says it was tested, but what OS's and capabilities were tested?  For example: 64-bit systems and 32-bit systems on what operating systems. And did those systems have
lseek64 and fseek64 while only being 32-bit and supporting LFS?

In short, although I understand that as is there is a problem on certain kinds of OS's (32-bit i586-pc-linux-gnu without or with LFS support?), but I am also concerned that because of the simplifications, there is a possibility that this patch breaks things on other systems, such as those that <heitbaum> did not test on.

With patch applied:

=================================================================
Testsuite summary for libcdio 2.1.0
=================================================================
# TOTAL: 16
# PASS:  9
# SKIP:  7
# XFAIL: 0
# FAIL:  0
# XPASS: 0
# ERROR: 0
=================================================================