Here is an excellent doc.

Tool chains have a loose name convention like arch [-vendor] [-os] - eabi

 arch -    refers to target architecture (which in our case is ARM)
 vendor -  refers to toolchain supplier
 os -      refers to the target operating system
 eabi -    refers to Embedded Application Binary Interface

some illustrations as follows :

• arm-none-eabi - This tool chain targets for ARM architecture, has no vendor, does not target an operating system and complies with the ARM EABI.
• arm-none-linux-gnueabi - This toolchain targets the ARM architecture, has no vendor, creates binaries that run on the Linux operating system, and uses the GNU EABI. It is used to target ARM-based Linux systems.

I would suggest to read those two articles, one from Arm, Instruction Set Architecture (-marm means that GCC will generate arm32/A32 code, -mthumb means that it will generate thumb/T32 one), and this research paper, Profile Guided Selection of ARM and ThumbInstructions.

Basically, the two instruction sets differ in the set of instructions available as well as their encoding. You should therefore get a smaller and faster executable by using thumb/T32 than by using arm/A32.

This is the reason why most of the tutorials recommend to use the thumb/T32 instruction set.

C++ requires that the math functions be part of the basic runtime while C allows them to be in a library. The GCC implementation achieved this by automatically linking libm in a C++ build.

There are many other differences in the link phase; C++ linking will consistently fail if a C linker is used.

For a C link, use the C linker and specify -lm to make libm available.

Providing information about the specific processor gives the compiler additional information for selecting the most efficient mix of instructions, and the most efficient way of scheduling those instructions. It depends very much on the specific processor how much performance difference explicitly specifying -mcpu makes. There could be no difference whatsoever - the only way to know is to measure.

But in general - if you are building a specific image for a specific device, then you should provide the compiler with as much information as possible.

Note: your current instance of gcc compiles assuming -march=armv4t - this is certainly not a universal guarantee for all arm gcc toolchains.