gcc: remove support for version 6.3.0

toolchain/gcc/Config.in

toolchain/gcc/Config.version

toolchain/gcc/common.mk

...n/gcc/patches/6.3.0/001-revert_register_mode_search.patch

toolchain/gcc/patches/6.3.0/002-case_insensitive.patch

toolchain/gcc/patches/6.3.0/010-documentation.patch

toolchain/gcc/patches/6.3.0/230-musl_libssp.patch

...gcc/patches/6.3.0/280-musl-disable-ifunc-by-default.patch

...in/gcc/patches/6.3.0/300-mips_Os_cpu_rtx_cost_model.patch

toolchain/gcc/patches/6.3.0/800-arm_v5te_no_ldrd_strd.patch

toolchain/gcc/patches/6.3.0/810-arm-softfloat-libgcc.patch

toolchain/gcc/patches/6.3.0/820-libgcc_pic.patch

toolchain/gcc/patches/6.3.0/830-arm_unbreak_armv4t.patch

...ain/gcc/patches/6.3.0/840-armv4_pass_fix-v4bx_to_ld.patch

toolchain/gcc/patches/6.3.0/850-use_shared_libgcc.patch

toolchain/gcc/patches/6.3.0/851-libgcc_no_compat.patch

toolchain/gcc/patches/6.3.0/870-ppc_no_crtsavres.patch

toolchain/gcc/patches/6.3.0/880-no_java_section.patch

toolchain/gcc/patches/6.3.0/881-no_tm_section.patch

toolchain/gcc/patches/6.3.0/900-bad-mips16-crt.patch