Fix invalid version .so links in Makefile

[clemensg]

The links to the .so files previously used a ${settings.core_version.major} suffix for C, C++ and C#, which is incorrect.
Instead append the core major version for C, the cpp major version for C++ and the csharp major version for C# links.

This fixes an "error while loading shared libraries .. cannot open shared object file.." on an embedded Linux application which was linked dynamically to libgrpc++.

[grpc-testing]

****************************************************************

libgrpc.so

     VM SIZE        FILE SIZE
 ++++++++++++++  ++++++++++++++

  [ = ]       0        0  [ = ]


****************************************************************

libgrpc++.so

     VM SIZE        FILE SIZE
 ++++++++++++++  ++++++++++++++

  [ = ]       0        0  [ = ]

[grpc-testing]

[trickle] No significant performance differences

[grpc-testing]

Objective-C binary sizes
*****************STATIC******************
  New size                      Old size
 1,965,242      Total (=)      1,965,242

 No significant differences in binary sizes

***************FRAMEWORKS****************
  New size                      Old size
10,909,026      Total (>)     10,909,023

 No significant differences in binary sizes

[grpc-testing]

[microbenchmarks] No significant performance differences

[clemensg]

Hi, I don't think that these three CI builds failed due to my changes. Is it possible to retry the build?

[clemensg]

Gentle ping @nicolasnoble @jtattermusch

[clemensg]

I reran generate_projects.sh and fixed-up the "Regenerate projects" commit in this PR to apply cleanly on top of the current master branch.

[clemensg]

Over a month passed since I created this PR. No response? @jtattermusch @nicolasnoble

[grpc-testing]

****************************************************************

libgrpc.so

     VM SIZE        FILE SIZE
 ++++++++++++++  ++++++++++++++

  [ = ]       0        0  [ = ]


****************************************************************

libgrpc++.so

     VM SIZE        FILE SIZE
 ++++++++++++++  ++++++++++++++

  [ = ]       0        0  [ = ]

[grpc-testing]

Objective-C binary sizes
*****************STATIC******************
  New size                      Old size
 2,019,964      Total (=)      2,019,964

 No significant differences in binary sizes

***************FRAMEWORKS****************
  New size                      Old size
11,183,090      Total (<)     11,183,093

 No significant differences in binary sizes

[grpc-testing]

Corrupt JSON data (indicates timeout or crash): 
    bm_call_create.BM_IsolatedFilter_ClientChannelFilter_NoOp_.counters.new: 10
    bm_call_create.BM_IsolatedFilter_ClientChannelFilter_NoOp_.counters.old: 10


[microbenchmarks] No significant performance differences

[jtattermusch]

Known failures (not related to this PR):
#17218
#17138

[jtattermusch]

Summary:
It seems that the SONAME of the shared libraries was adjusted in #10303 (which was only a partial fix for #10299), so the SONAME is now set to C++ major version but, the symlinks to that library are still created using the C-core version.

E.g.

$ objdump -p libgrpc++.so.1.17.0-dev | grep SONAME
SONAME               libgrpc++.so.1
# but a symlink libgrpc++.so.7  is created instead.

The PR seems to correctly fix the problem, thanks for the fix!

[jtattermusch]

FTR, the expression ${settings.get(lang_to_var[lib.language].lower() + '_version').major} is taken from https://github.com/grpc/grpc/pull/10303/files#diff-7b747c345348de73c8376cf79e5958f3R1562 (and that seems correct).

[jtattermusch]

LGTM.