Detect TARGET, CC, HOSTCC, FC automically when cross-compiling

[Dirreke]

Close #126

If OPENBLAS_{TARGET, CC, FC, HOSTCC} is not specified during cross-compilation, openblas-build will default to using the basic target that corresponds to the target architecture. However, please be advised that not all default targets are predefined and may not run correctly due to my limited knowledge of every potential target. The default values that are set are listed below:

"aarch64" => Some(Target::ARMV8),
"arm" => Some(Target::ARMV6),
"armv5te" => Some(Target::ARMV5),
"armv6" => Some(Target::ARMV6),
"armv7" => Some(Target::ARMV7),
"loongarch64" => Some(Target::LOONGSONGENERIC),
"mips64" => Some(Target::MIPS64_GENERIC),
"mips64el" => Some(Target::MIPS64_GENERIC),
"riscv64" => Some(Target::RISCV64_GENERIC),
"csky" => Some(Target::CK860FV),
"sparc" => Some(Target::SPARCV7),

This PR detect CC, HOSTCC by cc crate, and detect FC through CC