[llvm] [LLVM][Cygwin] Fix llvm-config shared library names (PR #136599)

[via llvm-commits]

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@@ -64,7 +64,11 @@ set(LLVM_CFLAGS "${LLVM_C_STD_FLAG} ${LLVM_DEFINITIONS}")
 set(LLVM_CXXFLAGS "${CMAKE_CXX${CMAKE_CXX_STANDARD}_STANDARD_COMPILE_OPTION} ${LLVM_CXX_STDLIB_FLAG} ${COMPILE_FLAGS} ${LLVM_DEFINITIONS}")
 set(LLVM_BUILD_SYSTEM cmake)
 set(LLVM_HAS_RTTI ${LLVM_CONFIG_HAS_RTTI})
-set(LLVM_DYLIB_VERSION "${LLVM_VERSION_MAJOR}${LLVM_VERSION_SUFFIX}")
+if(CYGWIN)
+  set(LLVM_DYLIB_VERSION "${LLVM_VERSION_MAJOR}.${LLVM_VERSION_MINOR}${LLVM_VERSION_SUFFIX}")
+else()
+  set(LLVM_DYLIB_VERSION "${LLVM_VERSION_MAJOR}${LLVM_VERSION_SUFFIX}")
+endif()
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jeremyd2019 wrote:

I was just looking at @tyan0's patches for proposed Cygwin patches and saw:
```patch
--- origsrc/llvm-20.1.2.src/tools/llvm-shlib/CMakeLists.txt	2025-04-11 08:58:02.655364700 +0900
+++ src/llvm-20.1.2.src/tools/llvm-shlib/CMakeLists.txt	2025-04-11 23:15:33.171264700 +0900
@@ -33,7 +33,7 @@ if(LLVM_BUILD_LLVM_DYLIB)
   if (LLVM_LINK_LLVM_DYLIB)
     set(INSTALL_WITH_TOOLCHAIN INSTALL_WITH_TOOLCHAIN)
   endif()
-  if (WIN32)
+  if (WIN32 OR CYGWIN)
     add_llvm_library(LLVM SHARED DISABLE_LLVM_LINK_LLVM_DYLIB SONAME ${INSTALL_WITH_TOOLCHAIN} ${SOURCES})
   else()
     add_llvm_library(LLVM SHARED DISABLE_LLVM_LINK_LLVM_DYLIB OUTPUT_NAME LLVM ${INSTALL_WITH_TOOLCHAIN} ${SOURCES})
```

This is what I am trying now to see if that makes the output look like MinGW.

https://github.com/llvm/llvm-project/pull/136599