Buildsystem does not allow a c and assembly source with the same name

[perigoso]

Buildsystem does not allow a c and assembly source with the same name, where only one is supposed to be compiled.

I found this issue while trying to implement an example for the efm32 family in #749.

The Cmsis provided by silabs as both a c implementation and an assembly implementation for the startup, only one should be compiled, but the buildsystem right now tries to compile both, regardless of which is included.

I have followed up the issue and think it is in rules.MK where both c and s files are compiled into a single object list, then when the objects are called for compilation, it resolves to both a c file and a s file.

I will be working on a fix soon.

[hathach]

this is indeed tricky, maybe we could auto add suffix _asm or _s into the object file of .S file in the rule.
https://github.com/hathach/tinyusb/blob/master/examples/rules.mk#L55 . I will also try to make an PR to fix this as well

[perigoso]

You PR looks good! I just tested it and got a successful build.