Compie different source code needs different tools

Compie different source code needs different compiling tools

Compie different source code needs different compiling tools ?
When I am reading the makefiles included in the or1k package,I found that different source code using different compiling tools.As follows:

source file dir       compiling tools
\or1k\uclinux\uC-libc:  
                  or32-elf-ranlib

\or1k\uclinux\userland\route:
          CC = or32-uclibc-gcc
          LD = or32-uclibc-gcc
         
\or1k\uclinux\uClinux-2.0.x:
CROSS_COMPILE    =or32-rtems-
AS    =$(CROSS_COMPILE)as
LD    =$(CROSS_COMPILE)ld
CC    =$(CROSS_COMPILE)gcc -D__KERNEL__ -I$(HPATH)

\or1k\linux\linux-2.4:
CROSS_COMPILE    = or32-uclinux-
AS        = $(CROSS_COMPILE)as
LD        = $(CROSS_COMPILE)ld
CC        = $(CROSS_COMPILE)gcc
My question is:
When we compile different source code(application,the kernel of uclinux,uclibc),the compiling tools must be different?
In my opinion,the compiling tools lie with   ISA(Instruction Set Architecture) and programming language. It has nothing to do with source code if the source is written by the same language.
Please give me hints, thanks in advance!

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