Condition split handshake tests on Linux in CMake.

This matches the source, which only builds support for these tests on
Linux. Note Android sets CMAKE_SYSTEM_NAME to "Android", so this covers
the previous ANDROID check.

Bug: 476
Change-Id: I41ca408706d0d0c5bb22006f4c31d51fc1267f69
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/51165
Commit-Queue: David Benjamin <davidben@google.com>
Reviewed-by: Adam Langley <agl@google.com>
Commit-Queue: Adam Langley <agl@google.com>
diff --git a/CMakeLists.txt b/CMakeLists.txt
index 36bc8ec..c64ba8e 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -618,7 +618,7 @@
   endif()
 endif()
 
-if(UNIX AND NOT APPLE AND NOT ANDROID)
+if(CMAKE_SYSTEM_NAME STREQUAL "Linux")
   set(HANDSHAKER_ARGS "-handshaker-path" $<TARGET_FILE:handshaker>)
 endif()
 
diff --git a/ssl/test/CMakeLists.txt b/ssl/test/CMakeLists.txt
index bb9bd81..f02d6e2 100644
--- a/ssl/test/CMakeLists.txt
+++ b/ssl/test/CMakeLists.txt
@@ -17,7 +17,7 @@
 
 target_link_libraries(bssl_shim test_support_lib ssl crypto)
 
-if(UNIX AND NOT APPLE AND NOT ANDROID)
+if(CMAKE_SYSTEM_NAME STREQUAL "Linux")
   add_executable(
     handshaker