asm support: adapt to changes in CMakeDetectCompiler in 2.8.10

This fixes #14210. In 2.8.10 CMakeDetermineCompiler.cmake was
modified (or added), and now the _INIT variable must not
be set to a list anymore, before it worked.

Alex
Merge topic 'FixAsmSupport' into next

e7722fd asm support: adapt to changes in CMakeDetectCompiler in 2.8.10