fix the shared tbb link on rtools42 and aarch64 windows

Two failures from the first CI run, both only reachable now that TBB is linked
as a shared library on Windows -- a static build has no link step.

Rtools42 (gcc 10): the TBB link failed with undefined references to
__stack_chk_fail, __strncpy_chk and __strncat_chk. TBB compiles with
-fstack-protector-strong and _FORTIFY_SOURCE, and on mingw those helpers live
in libssp rather than libgcc; newer toolchains pull it in implicitly, Rtools42
does not. Pass -lssp via CMAKE_SHARED_LINKER_FLAGS, mirroring the -lssp that
configure.R already adds for RcppParallel's own link.

aarch64 Windows: 'lld: error: unknown argument: -z'. Rtools45-aarch64 drives
clang with lld, and Clang.cmake adds -Wl,-z,relro,-z,now for any non-Apple
target. GNU.cmake already guards this with NOT MINGW; give Clang.cmake the
equivalent guard.

windows-latest (release) passed on the first run, so the shared mingw build,
the PREFIX "" naming and the reordered load in .onLoad() all work.

Author: kevinushey

patches/mingw_clang_cmake.diff

@@ -0,0 +1,17 @@
+--- a/src/tbb/cmake/compilers/Clang.cmake
++++ b/src/tbb/cmake/compilers/Clang.cmake
+@@ -65,8 +65,12 @@ endif()
+ # Clang flags to prevent compiler from optimizing out security checks
+ set(TBB_COMMON_COMPILE_FLAGS ${TBB_COMMON_COMPILE_FLAGS} -Wformat -Wformat-security -Werror=format-security -fPIC $<$<NOT:$<BOOL:${EMSCRIPTEN}>>:-fstack-protector-strong>)
+ 
+-# -z switch is not supported on MacOS
+-if (NOT APPLE)
++# -z switch is not supported on MacOS or on Windows. The Windows guard is a
++# local addition, mirroring the one GNU.cmake already carries: Rtools for
++# aarch64 Windows drives clang with lld, which rejects the option outright
++# ("lld: error: unknown argument: -z"). Only reachable now that we build TBB
++# as a shared library there, since a static build has no link step.
++if (NOT APPLE AND NOT WIN32)
+     set(TBB_LIB_LINK_FLAGS ${TBB_LIB_LINK_FLAGS} -Wl,-z,relro,-z,now)
+ endif()
+ 

src/install.libs.R

@@ -315,6 +315,12 @@ useBundledTbb <- function() {
    if (.Platform$OS.type == "windows") {
       cmakeFlags <- c(
          "-G", "MSYS Makefiles",
+         # TBB compiles with -fstack-protector-strong and _FORTIFY_SOURCE, and
+         # on mingw the helpers those need (__stack_chk_fail, __strncpy_chk and
+         # friends) live in libssp rather than in libgcc. Newer toolchains pull
+         # it in implicitly; Rtools42 (gcc 10) does not, and the TBB link then
+         # fails with undefined references to them
+         "-DCMAKE_SHARED_LINKER_FLAGS=-lssp",
          cmakeFlags
       )
    }

src/tbb/cmake/compilers/Clang.cmake

@@ -65,8 +65,12 @@ endif()
 # Clang flags to prevent compiler from optimizing out security checks
 set(TBB_COMMON_COMPILE_FLAGS ${TBB_COMMON_COMPILE_FLAGS} -Wformat -Wformat-security -Werror=format-security -fPIC $<$<NOT:$<BOOL:${EMSCRIPTEN}>>:-fstack-protector-strong>)
 
-# -z switch is not supported on MacOS
-if (NOT APPLE)
+# -z switch is not supported on MacOS or on Windows. The Windows guard is a
+# local addition, mirroring the one GNU.cmake already carries: Rtools for
+# aarch64 Windows drives clang with lld, which rejects the option outright
+# ("lld: error: unknown argument: -z"). Only reachable now that we build TBB
+# as a shared library there, since a static build has no link step.
+if (NOT APPLE AND NOT WIN32)
     set(TBB_LIB_LINK_FLAGS ${TBB_LIB_LINK_FLAGS} -Wl,-z,relro,-z,now)
 endif()