[C++][regression] Error when building Arrow v18.0.0 against non-LTS absl, abseil-cpp

[gorloffslava]

Describe the bug, including details regarding any error messages, version, and platform.

What causes the issue?

1. When absl is built from the master and not from the tagged release, it doesn't define LTS_VERSION.
2. Consequently, when CMake finds the non-LTS absl installation, the absl_VERSION variable is not set.
3. And when we check this variable here, it expands to an empty string, which, in turn, leads to the cryptic error message:

CMake Error at cmake_modules/ThirdpartyToolchain.cmake:315 (if):
if given arguments:
 
     "VERSION_LESS" "20211102"
 
   Unknown arguments specified
 Call Stack (most recent call first):
   cmake_modules/ThirdpartyToolchain.cmake:4166 (resolve_dependency)
   CMakeLists.txt:546 (include)

Why it's the regression?

1. Arrow v17.0.0 builds successfully against non-LTS absl.
2. The code that added the failing check was introduced in e65c1e2

Temporary workaround:

1. By manually passing -Dabsl_VERSION=<some lts version, like '20240722.0'> bypasses the check.
2. However, this workaround is dirty. If one day will rely on this version for more granular check, it may break the things.

Why it's important?

1. absl themselves encourage people to use cutting-edge version built from the latest commit, so it will cause problems for many Arrow consumers.

Component(s)

C++

[assignUser]

cc @kou @raulcd

absl themselves encourage people to use cutting-edge version built from the latest commit, so it will cause problems for many Arrow consumers.

Even though there is a workaround I think this is a valid concern that might warrant inclusion in the new patch/minor?

@gorloffslava can you test with my changes in #44613