OSL v1.13.9.0

Release 1.13.9.0 -- 1 May 2024 (compared to 1.13.8.0)

• deps: Support for LLVM-18 #1773 (by مهدي شينون (Mehdi Chinoune) #1803 (by Larry Gritz)
• fix: Make isconnected() work with downstream renderer "connections." #1782 (by sfriedmapixar)
• cleanup: Change OSL_CONSTEXPR14 to constexpr #1805
• internals build: Fix ifdef typo #1804
• build: Propagate cpp version #1797
• build: Print commit hash of locally built dependencies #1798
• ci: Lock down to OIIO 2.5 for icc tests #1799
• ci: Suppress leak sanitizer warnings about internals of robin_hash #1807
• docs: More detail about supported platforms in INSTALL.md #1796