Add support for Alpine Linux (#7440)

This change enables build of CoreCLR on Alpine Linux. Here is the list
of changes:
- Disable asserts checking RSP in arbitrary threads against cached stack limit
  for the respective thread. The stack on Alpine obviously grows over the limit
  reported by the pthread functions.
- Disable using XSTATE. This should be re-enabled after MUSL gets the _xstate,
  _fpx_sw_bytes and related data structures added to the signal.h header.
- Disable setting rlimit of RLIMIT_NOFILE to the max value, since it breaks
  debugging for some reason.
- Add skipping over the hardware signal trampoline in the PAL_VirtualUnwind.
  While we were not trying to walk over it in a simple case, in a case where
  an exception was thrown from a catch handler of a hardware exception, we
  still attempted to walk over it and it fails on Alpine.
- Fix detection of Alpine Linux in the PAL's CMakeLists.txt so that it works
  in Docker containers too.
- Modified PAL_VirtualUnwind to make the check for unwinding past the bottom
  of the stack unconditional. We had a long list of platforms where we were
  doing this check and it doesn't hurt to do it on platforms where it is not
  needed. I have done that rather than adding a check for Alpine Linux as
  another platform that needs it.

1 files changed, 6 insertions, 0 deletions

diff --git a/clrdefinitions.cmake b/clrdefinitions.cmake
index e088f12472..135e8c2c6e 100644
--- a/clrdefinitions.cmake
+++ b/clrdefinitions.cmake
@@ -61,6 +61,12 @@ if (CLR_CMAKE_PLATFORM_UNIX)
 
 endif(CLR_CMAKE_PLATFORM_UNIX)
 
+if(CLR_CMAKE_PLATFORM_ALPINE_LINUX)
+  # Alpine Linux doesn't have fixed stack limit, this define disables some stack pointer
+  # sanity checks in debug / checked build that rely on a fixed stack limit
+  add_definitions(-DNO_FIXED_STACK_LIMIT)
+endif(CLR_CMAKE_PLATFORM_ALPINE_LINUX)
+
 add_definitions(-D_BLD_CLR)
 add_definitions(-DDEBUGGING_SUPPORTED)
 add_definitions(-DPROFILING_SUPPORTED)