Fix PR35739: chkstk and chkst2 should only be built for Windows

As reported in PR35739, rL252927 added the Windows specific chkstk and
chkstk2 sources unconditionally, and since these are assembly without a
NO_EXEC_STACK_DIRECTIVE at the end, automated vulnerability scanners
warned about the objects having an executable stack.

Avoid the problem by only including these files when Windows is
targeted.

Reviewers: compnerd, rnk, martell

Reviewed By: martell

Subscribers: mstorsjo, mgorny, martell, javed.absar, #sanitizers, llvm-commits

Differential Revision: https://reviews.llvm.org/D41567

llvm-svn: 321431

compiler-rt/lib/builtins/CMakeLists.txt

@@ -232,8 +232,6 @@ set(x86_ARCH_SOURCES
 
 if (NOT MSVC)
   set(x86_64_SOURCES
-      x86_64/chkstk.S
-      x86_64/chkstk2.S
       x86_64/floatdidf.c
       x86_64/floatdisf.c
       x86_64/floatdixf.c
@@ -253,8 +251,6 @@ if (NOT MSVC)
   set(i386_SOURCES
       i386/ashldi3.S
       i386/ashrdi3.S
-      i386/chkstk.S
-      i386/chkstk2.S
       i386/divdi3.S
       i386/floatdidf.S
       i386/floatdisf.S