Kernel/LibC: Add crt* files to LibC and remove crt0 from kernel

There was no reason for libc get crt0 from kernel.

libc/arch/x86_64/crt0.S

@@ -0,0 +1,35 @@
+.section .text
+
+.global _start
+_start:
+	# Set up end of the stack frame linked list.
+	movq $0, %rbp
+	pushq %rbp # rip=0
+	pushq %rbp # rbp=0
+	movq %rsp, %rbp
+
+	# Save argc, argv, environ
+	pushq %rdx
+	pushq %rsi
+	pushq %rdi
+
+	# Prepare malloc, environment
+	movq %rdx, %rdi
+	call _init_libc
+
+	# Call global constructos
+	call _init
+
+	# Restore argc, argv, environ
+	popq %rdi
+	popq %rsi
+	popq %rdx
+
+	# Run main
+	call main
+
+	# Cleanly exit the process
+	movl %eax, %edi
+	call exit
+
+.size _start, . - _start

libc/arch/x86_64/crti.S

@@ -0,0 +1,16 @@
+/* x86-64 crti.s */
+.section .init
+.global _init
+.type _init, @function
+_init:
+	pushq %rbp
+	movq %rsp, %rbp
+	/* gcc will nicely put the contents of crtbegin.o's .init section here. */
+
+.section .fini
+.global _fini
+.type _fini, @function
+_fini:
+	pushq %rbp
+	movq %rsp, %rbp
+	/* gcc will nicely put the contents of crtbegin.o's .fini section here. */

libc/arch/x86_64/crtn.S

@@ -0,0 +1,10 @@
+/* x86-64 crtn.s */
+.section .init
+	/* gcc will nicely put the contents of crtend.o's .init section here. */
+	popq %rbp
+	ret
+
+.section .fini
+	/* gcc will nicely put the contents of crtend.o's .fini section here. */
+	popq %rbp
+	ret