In early years the options for developing software for #Amiga in C meant using a commercial compiler: Manx Aztec C or Lattice C (later SAS/C). Most commonly the C compiler was pirated due to the aspiring devs being just bunch of kids.
Soon Matt Dillon released his freeware DICE C - liberating amiga development from having to resort to commercial software (or piracy). While DICE C wasn't bad by any measure, it wasn't open source, and I remember experiencing some issues with it and having to switch back to SAS/C. Many existing amiga C code targeted Lattice / SAS C and used its amiga specific extensions, making use of DICE bit of a pain.
Around the same time Markus Wild & co created Geek Gadgets (GG) / Amiga Developer Environment (ADE). Rather than writing a full new development tools they opted to porting BSD / #GNU ones: Their #POSIX compatibility library ixemul allowed relatively easy porting of existing tools (mostly ./configure && make - sometimes requiring some minor patches). This allowed use of GNU C compiler (gcc) and other standard GNU tools. However, gcc was way too large and heavy for basic A500 systems.
Later Volker Barthelmann's #VBCC project introduced yet another open source option.
In #MorphOS we use highly expanded ixemul library and latest GNU toolchains (I've ported all recent GCC versions and binutils 2.42).