[Bug-readline] Set correct -compatibility_version in .dylib on Mac OS X

[Max Horn]

Hi there,

the first patch reformats the shobj-conf code for OS X a bit, and reduces code 
duplication while hopefully improving readability.

The second patch then drops the useless "-v" flag (it just causes the linker to 
prints its version), and then tweaks the compatibility_version to match the 
current_version.

The rationale behind this is the following: The purpose of the 
compatibility_version is to reflect when new ABIs are added. Since readline 6.3 
added new ABI compared to 6.2, it should have higher compatibility_version. 

With this in place, a binary linked against readline 6.2 will work fine with 
6.3; but one linked against 6.3 will refuse to run with just readline 6.2 
present. This is the correct and desired behavior. Without this patch, a binary 
that relies on 6.3 specific API / ABI extensions could be executed even if only 
readline 6.2 was installed, leading to unexpected runtime crashes of the binary.



As a side note: The current_version should always be greater or equal than the 
compatibility_version; the only reason for those to differ (that I am aware of) 
is to allow client code to determine the precise version of the loaded shared 
library, e.g. to determine if it has a patch level that avoids a known bug etc. 
that is independent of the ABI version.

However, the patch level is not visible to the build code, so for readline, the 
compatibility_version and current_version simply are always equal.


Cheers,
Max

0001-refactor-shobj-conf-to-improve-readability.patch
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0002-drop-useless-v-linker-flag-fix-compatibility_version.patch
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