Revert versioning changes in library SONAMEs

Summary:
This reverts the following upstream commits:
- llvm@91a3846
- llvm@10c48a7

which change how SONAMEs for toolchain libraries are created. This change has the potential to [break existing applications (such as coredumper)](D54233371) that rely on, e.g., `/opt/llvm/compat/lib/liblldb.15.so` as it no longer exists  - in favor of `liblldb.15.so.0`.

---

Reverted the commits mentioned above by doing:
```
$ git show 10c48a7 | git apply -R
$ git show 91a3846 | git apply -R
```

Test Plan:
Built the toolchain:
```
make DESTDIR=$PWD/install/Prod/usr BuildType=Release+Distribution toolchain
```
and confirmed that the .so names follow the old pattern:
```
$ ls install/Prod/usr/lib/
clang  libclang.so     libclang.so.15.0.0  liblldb.so.15      libLTO.so     libmimalloc.so    libmimalloc.so.2.0  python3.10
cmake  libclang.so.15  liblldb.so          liblldb.so.15.0.0  libLTO.so.15  libmimalloc.so.2  pkgconfig           python3.8
```

Reviewers: wanyi, hyubo, #lldb_team

Reviewed By: hyubo

Subscribers: pdepetro, #lldb_team

Differential Revision: https://phabricator.intern.facebook.com/D54286076

Author: aperez

llvm/CMakeLists.txt

@@ -28,7 +28,7 @@ endif()
 
 if(NOT DEFINED LLVM_SHLIB_SYMBOL_VERSION)
   # "Symbol version prefix for libLLVM.so"
-  set(LLVM_SHLIB_SYMBOL_VERSION "LLVM_${LLVM_VERSION_MAJOR}.${LLVM_VERSION_MINOR}")
+  set(LLVM_SHLIB_SYMBOL_VERSION "LLVM_${LLVM_VERSION_MAJOR}")
 endif()
 
 if ((CMAKE_GENERATOR MATCHES "Visual Studio") AND (MSVC_TOOLSET_VERSION LESS 142) AND (CMAKE_GENERATOR_TOOLSET STREQUAL ""))

llvm/cmake/modules/AddLLVM.cmake

@@ -123,7 +123,7 @@ function(add_llvm_symbol_exports target_name export_file)
       COMMAND "${Python3_EXECUTABLE}" "-c"
       "import sys; \
        lines = ['    ' + l.rstrip() for l in sys.stdin] + ['  local: *;']; \
-       print('LLVM_${LLVM_VERSION_MAJOR}.${LLVM_VERSION_MINOR} {'); \
+       print('LLVM_${LLVM_VERSION_MAJOR} {'); \
        print('  global:') if len(lines) > 1 else None; \
        print(';\\n'.join(lines) + '\\n};')"
       < ${export_file} > ${native_export_file}
@@ -723,9 +723,9 @@ function(llvm_add_library name)
     if(UNIX AND NOT APPLE AND NOT ARG_SONAME)
       set_target_properties(${name}
         PROPERTIES
-        # Since 18.1.0, the ABI version is indicated by the major and minor version.
-        SOVERSION ${LLVM_VERSION_MAJOR}.${LLVM_VERSION_MINOR}${LLVM_VERSION_SUFFIX}
-        VERSION ${LLVM_VERSION_MAJOR}.${LLVM_VERSION_MINOR}${LLVM_VERSION_SUFFIX})
+        # Since 4.0.0, the ABI version is indicated by the major version
+        SOVERSION ${LLVM_VERSION_MAJOR}${LLVM_VERSION_SUFFIX}
+        VERSION ${LLVM_VERSION_MAJOR}${LLVM_VERSION_SUFFIX})
     endif()
   endif()
 

llvm/tools/llvm-shlib/CMakeLists.txt

@@ -190,5 +190,5 @@ if(LLVM_BUILD_LLVM_C_DYLIB AND MSVC)
     # Make sure we search LLVMSupport first, before the CRT libs
     set(CMAKE_SHARED_LINKER_FLAGS "${CMAKE_SHARED_LINKER_FLAGS} -INCLUDE:malloc")
   endif()
-  
+
 endif()