cmake: only build tst fixtures when ENABLE_TESTS is on

The tst_base fixture library links GTest::gtest, but that imported
target only exists when find_package(GTest) runs, which is guarded by
ENABLE_TESTS. add_subdirectory(tst) was unconditional, so a -no-tests
build failed at generate time with 'Target tst_base links to
GTest::gtest but the target was not found'.

Guard add_subdirectory(tst) with ENABLE_TESTS. This is safe because
every consumer of tst/tst_base/tst_integrated_fixture lives in a
test/cpp directory that is itself gated by ENABLE_TESTS.

Signed-off-by: Matt Liberty <mliberty@precisioninno.com>

Author: maliberty

src/CMakeLists.txt

@@ -255,7 +255,11 @@ if (NOT USE_SYSTEM_OPENSTA)
 endif()
 add_subdirectory(dbSta)
 add_subdirectory(rsz)
-add_subdirectory(tst)
+if(ENABLE_TESTS)
+  # tst provides gtest-based fixture libraries used only by test targets, and
+  # links GTest::gtest, which only exists when ENABLE_TESTS is on.
+  add_subdirectory(tst)
+endif()
 add_subdirectory(stt)
 add_subdirectory(gpl)
 add_subdirectory(dpl)