Reorgsv2 😜

[zocterminal]

2nd attempt to reorganize source code to consolidate copied functions:

Compared to the first "reorgs" pull request (https://github.com/karpathy/llm.c/pull/174) this is a minimalistic approach. Only the most obvious candidates were put into a c-file and then pulled in from the main sources via #include.

• common stuff is now in train_common.c and train_common.h
• train_common.h is not strictly necessary, but will make it easier to move away from the #include approach and compile separately (see the old "reorgs" (https://github.com/karpathy/llm.c/pull/174) how that would be done)
• made use the checkFopen(), mallocCheck() etc. functions in train_gpt2.c also.

It would be possible to move the GPT2 structs into train_common.h also. The differences there between the files are marginal and would require only miniscule use of #ifdefs, but I didn't do that (based on the comments in the prior "reorgs" pull request). The structs GPT2Config and ParameterTensors tensors are even identical between .c and .cu.

Enjoy.