[Comgr] Specifiy C99 in the README

Author: lamb-j

amd/comgr/README.md

@@ -3,6 +3,7 @@ Code Object Manager (Comgr)
 
 The Comgr library provides APIs for compiling and inspecting AMDGPU code
 objects. The API is documented in the [header file](include/amd_comgr.h.in).
+The Comgr API is compatible with C99 and C++.
 
 Building the Code Object Manager
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