cgen: Don't emit mman.h and pthreads related code for freestanding bu…

[raw-bin]

• This PR addresses an issue encountered with freestanding builds used for bare metal embedded targets that use anonymous functions.
• The issue is to do with the code generated for closure management - which are inherently associated with anonymous functions. The closure management code assumes that the run-time environment has support for mmap and posix locking primitives.
• Mmap and posix locking primitives are typically not available on bare metal embedded systems.
• This PR ensures that the generated code for closure managment doesn't contain mmap and posix locking for freestanding builds.
• Although this code solves the immediate problem a proper solution needs to parameterise things like page size assumptions etc.
• Unfortunately I could not figure out how to write a test for freestanding builds just yet.

[huly-for-github]

Connected to Huly®: V_0.6-22509

[spytheman]

Suggested change

	if pref_.os != .windows && pref_.is_bare == false {
	if pref_.os != .windows && !pref_.is_bare {

[spytheman]

Unfortunately I could not figure out how to write a test for freestanding builds just yet.

You can put a pair of .vv/.out files in vlib/v/gen/c/testdata/ , then run:
./v vlib/v/gen/c/coutput_test.v .

Note: the .vv file has to start with:
// vtest vflags: -cc gcc -freestanding .
The corresponding .out file should contain the output of the .vv program, which will be compiled with the flags in that comment.

See for example https://github.com/vlang/v/blob/master/vlib/v/gen/c/testdata/freestanding_module_import_2.vv .