For aligned_realloc, you may want to look at using jemalloc for your code, instead of the vendor malloc. It's got an "experimental" function rallocm that does allow you to choose the alignment. Regarding m4 as a preprocessor, I'd rather wishlist a proper macro system for Cx+n that could do the job of the preprocessor and any other uses of precompiling.
The big problem with extending the C language is that C's in a ton of places. Some of the things you describe would mean increasing the size of the C runtime, which would be unacceptable in embedded programming and the like. Perhaps we need a middle ground language here -- more daring than C, more conservative than C++ -- where ideas can be tuned better and/or be specified for system types. C's universal assembly role really is a double edged sword as far as getting new stuff in the language.
The big problem with extending the C language is that C's in a ton of places. Some of the things you describe would mean increasing the size of the C runtime, which would be unacceptable in embedded programming and the like. Perhaps we need a middle ground language here -- more daring than C, more conservative than C++ -- where ideas can be tuned better and/or be specified for system types. C's universal assembly role really is a double edged sword as far as getting new stuff in the language.