use -fno-strict-aliasing for code using COM pointers

Following the discussion in !869 (merged) it might not be safe to cast to void** to get pointer values and thus using IID_PPV_ARGS or WRL. Using -fno-strict-aliasing should allow us to use this helpful Windows/compiler API's.

This might be backported to 3.0 where COM and WRL are used.

v2:

• C++ modules only
• renamed to LIBCOMFLAGS

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v3:

• added freetype/dwrite which uses WRL and COM without LIBCOM (DWriteCreateFactory)
• split the general commit using LIBCOMFLAGS so they can be backported to 3.0 independently

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v4:

• test -fno-strict-aliasing with the C++ compiler, not the C compiler

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v5:

• fix missing AM_CXXFLAGS for dwrite

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v8:

• have -fno-strict-aliasing on Windows or fail configure 💥
• renamed the flag to LIBCOMCXXFLAGS to show it should be used in C++ code, the fancy C++ helpers are not available there, the code will have to be clean from pointer aliasing with COM objects.