[Build] Fix dependency problems when bootstrapping.

If we're bootstrapping *and* skip-early-swiftsyntax is enabled, the
build can fail while trying to build target executables because we
haven't built a copy of libswiftCore yet but *the compiler* refers
to it.

This is "fixed" in other places by setting LD_LIBRARY_PATH, but we
don't want or need to do that here; we just want to delay building
these executables until after libswiftCore is available.

rdar://116485713

Author: al45tair

stdlib/cmake/modules/AddSwiftStdlib.cmake

@@ -2976,13 +2976,21 @@ function(add_swift_target_executable name)
           "-${SWIFT_SDK_${sdk}_LIB_SUBDIR}"
           SWIFTEXE_TARGET_DEPENDS_with_suffix)
 
+      # Note: we add ${swiftexe_link_libraries_targets} to the DEPENDS
+      # below because when --bootstrapping=bootstrapping with
+      # skip-early-swiftsyntax, the build system builds the Swift compiler
+      # but not the standard library during the bootstrap, and then when
+      # it tries to build swift-backtrace it fails because *the compiler*
+      # refers to a libswiftCore.so that can't be found.
+
       _add_swift_target_executable_single(
           ${VARIANT_NAME}
           ${SWIFTEXE_TARGET_NOSWIFTRT_keyword}
           ${SWIFTEXE_TARGET_SOURCES}
           DEPENDS
             ${SWIFTEXE_TARGET_DEPENDS_with_suffix}
             ${swiftexe_module_dependency_targets}
+            ${swiftexe_link_libraries_targets}
           SDK "${sdk}"
           ARCHITECTURE "${arch}"
           COMPILE_FLAGS