Fixes#61355. The __dso_handle decl was introduced incorrectly into the startup
objects during the integration test cleanup which moved the integration tests
away from using an artificial sysroot to using -nostdlib. Having it in the
startup creates the duplicate symbol error when one does not use -nostdlib.
Since this is an integration test only problem, it is meaningful to keep it in
the integration test anyway.
Differential Revision: https://reviews.llvm.org/D145898
Also, added riscv64 startup code for static linking which is used
by the integration tests. Functions from the C standard threads
library have been enabled.
Reviewed By: mikhail.ramalho
Differential Revision: https://reviews.llvm.org/D145670
