[clang] [llvm] Fix Singals compatibility with Cygwin API (PR #134494)

[Mateusz Mikuła via llvm-commits]

https://github.com/mati865 created https://github.com/llvm/llvm-project/pull/134494

With these changes, LLVM and Clang become buildable for Cygwin.

GCC config (using MSYS2 GCC):
`CFLAGS="-D_GNU_SOURCE=1" CXXFLAGS="-D_GNU_SOURCE=1" CPPFLAGS="-D_GNU_SOURCE=1" cmake -GNinja -DCMAKE_BUILD_TYPE=Release -DLLVM_ENABLE_PROJECTS="clang;lld" -DLLVM_DEFAULT_TARGET_TRIPLE=x86_64-pc-cygwin -DLLVM_HOST_TRIPLE=x86_64-pc-cygwin -DLLVM_TARGETS_TO_BUILD="AArch64;X86" -DLIBCLANG_BUILD_STATIC=ON ../llvm`

Clang config (using https://github.com/msys2/MSYS2-packages/pull/5308):
`CC=clang CXX=clang++ cmake -GNinja -DCMAKE_BUILD_TYPE=Release -DLLVM_ENABLE_PROJECTS="clang;lld" -DLLVM_DEFAULT_TARGET_TRIPLE=x86_64-pc-cygwin -DLLVM_HOST_TRIPLE=x86_64-pc-cygwin -DLLVM_TARGETS_TO_BUILD="AArch64;X86" -DLIBCLANG_BUILD_STATIC=ON ../llvm`

Split out from https://github.com/llvm/llvm-project/pull/134458

>From 17cbb1f99d281adfc83c7c7a250de31fd341db7a Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Mateusz=20Miku=C5=82a?= <oss at mateuszmikula.dev>
Date: Sat, 5 Apr 2025 13:18:35 +0200
Subject: [PATCH 1/4] [LLVM][Cygwin] Fix Singals compatibility with Cygwin API

---
 llvm/lib/Support/Unix/Signals.inc | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/llvm/lib/Support/Unix/Signals.inc b/llvm/lib/Support/Unix/Signals.inc
index 30e5f40193974..68a0e2d218e68 100644
--- a/llvm/lib/Support/Unix/Signals.inc
+++ b/llvm/lib/Support/Unix/Signals.inc
@@ -847,7 +847,11 @@ void llvm::sys::PrintStackTrace(raw_ostream &OS, int Depth) {
 
     const char *name = strrchr(dlinfo.dli_fname, '/');
     if (!name)
+#ifdef __CYGWIN__
+      OS << format(" %-*s", width, &dlinfo.dli_fname);
+#else
       OS << format(" %-*s", width, dlinfo.dli_fname);
+#endif
     else
       OS << format(" %-*s", width, name + 1);
 
@@ -884,6 +888,8 @@ void llvm::sys::DisableSystemDialogsOnCrash() {}
 /// When an error signal (such as SIGABRT or SIGSEGV) is delivered to the
 /// process, print a stack trace and then exit.
 void llvm::sys::PrintStackTraceOnErrorSignal(StringRef Argv0,
+
+
                                              bool DisableCrashReporting) {
   ::Argv0 = Argv0;
 

>From cd536e2c11fbbe68333569cf3a425eb546c99b27 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Mateusz=20Miku=C5=82a?= <oss at mateuszmikula.dev>
Date: Sat, 8 Feb 2025 13:57:49 +0100
Subject: [PATCH 2/4] [Clang][Cygwin] Fix symbol visibility definition

---
 clang/include/clang/Support/Compiler.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/clang/include/clang/Support/Compiler.h b/clang/include/clang/Support/Compiler.h
index 5a74f8e3b6723..e1ae3eda4ccc2 100644
--- a/clang/include/clang/Support/Compiler.h
+++ b/clang/include/clang/Support/Compiler.h
@@ -50,7 +50,7 @@
 #define CLANG_EXPORT_TEMPLATE
 #endif
 #elif defined(__ELF__) || defined(__MINGW32__) || defined(_AIX) ||             \
-    defined(__MVS__)
+    defined(__MVS__) || defined(__CYGWIN__)
 #define CLANG_ABI LLVM_ATTRIBUTE_VISIBILITY_DEFAULT
 #define CLANG_TEMPLATE_ABI LLVM_ATTRIBUTE_VISIBILITY_DEFAULT
 #define CLANG_EXPORT_TEMPLATE

>From 59dd21b97cc324be1eb4c28b4cdc0e4374df9463 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Mateusz=20Miku=C5=82a?= <oss at mateuszmikula.dev>
Date: Fri, 4 Apr 2025 15:08:18 +0200
Subject: [PATCH 3/4] [Clang][Cygwin] Disable shared libs on Cygwin by default

---
 clang/tools/CMakeLists.txt          | 5 +++--
 clang/tools/libclang/CMakeLists.txt | 2 +-
 2 files changed, 4 insertions(+), 3 deletions(-)

diff --git a/clang/tools/CMakeLists.txt b/clang/tools/CMakeLists.txt
index e3557c1328d53..0f4949f8d37a5 100644
--- a/clang/tools/CMakeLists.txt
+++ b/clang/tools/CMakeLists.txt
@@ -26,9 +26,10 @@ endif()
 add_clang_subdirectory(c-index-test)
 
 add_clang_subdirectory(clang-refactor)
-# For MinGW we only enable shared library if LLVM_LINK_LLVM_DYLIB=ON.
+# For MinGW/Cygwin we only enable shared library if LLVM_LINK_LLVM_DYLIB=ON.
 # Without that option resulting library is too close to 2^16 DLL exports limit.
-if(UNIX OR (MSVC AND LLVM_BUILD_LLVM_DYLIB_VIS) OR (MINGW AND LLVM_LINK_LLVM_DYLIB))
+if((UNIX AND NOT CYGWIN) OR (MSVC AND LLVM_BUILD_LLVM_DYLIB_VIS) OR
+  ((MINGW OR CYGWIN) AND LLVM_LINK_LLVM_DYLIB))
   add_clang_subdirectory(clang-shlib)
 endif()
 
diff --git a/clang/tools/libclang/CMakeLists.txt b/clang/tools/libclang/CMakeLists.txt
index 299c14660f3d4..ac7a9a8db37c0 100644
--- a/clang/tools/libclang/CMakeLists.txt
+++ b/clang/tools/libclang/CMakeLists.txt
@@ -106,7 +106,7 @@ if (LLVM_EXPORTED_SYMBOL_FILE)
                      DEPENDS ${LIBCLANG_VERSION_SCRIPT_FILE})
 endif()
 
-if(LLVM_ENABLE_PIC OR (WIN32 AND NOT LIBCLANG_BUILD_STATIC))
+if(LLVM_ENABLE_PIC OR ((WIN32 OR CYGWIN) AND NOT LIBCLANG_BUILD_STATIC))
   set(ENABLE_SHARED SHARED)
 endif()
 

>From ef352adb9035d61333674d4418e682f31c4e342b Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Mateusz=20Miku=C5=82a?= <oss at mateuszmikula.dev>
Date: Fri, 4 Apr 2025 21:41:50 +0200
Subject: [PATCH 4/4] [Clang][Cygwin] Remove erroneous define

---
 clang/tools/libclang/CIndexer.cpp | 1 -
 1 file changed, 1 deletion(-)

diff --git a/clang/tools/libclang/CIndexer.cpp b/clang/tools/libclang/CIndexer.cpp
index 12d9d418dea51..1b9d58bc439ad 100644
--- a/clang/tools/libclang/CIndexer.cpp
+++ b/clang/tools/libclang/CIndexer.cpp
@@ -29,7 +29,6 @@
 #ifdef __CYGWIN__
 #include <cygwin/version.h>
 #include <sys/cygwin.h>
-#define _WIN32 1
 #endif
 
 #ifdef _WIN32