A part of the safety story of any useful toolchain compliant to ISO 26262 as a SEOOC is that it verifiably implements the language as documented in the standard. The "verifiably" part is important. If there is no standard to verify against, how do you know it's doing the right thing?
The language standards themselves state outright that programs containing undefined behaviour are malformed. If you write malformed programs, you can not assume that they are safe. Don't blame language standardization for your writing bad, unsafe software if you're not going to follow it.
In addition verifiably conformant compilers for translating your programs into software, the standard allows other tools to be written to perform things like static analysis, complexity analysis, and conformance to other published guidelines (eg. MISRA). These things are not possible where the definition of the language is "whatever one single toolchain vendor decides it will be this week".
The language standards themselves state outright that programs containing undefined behaviour are malformed. If you write malformed programs, you can not assume that they are safe. Don't blame language standardization for your writing bad, unsafe software if you're not going to follow it.
In addition verifiably conformant compilers for translating your programs into software, the standard allows other tools to be written to perform things like static analysis, complexity analysis, and conformance to other published guidelines (eg. MISRA). These things are not possible where the definition of the language is "whatever one single toolchain vendor decides it will be this week".