* zfh zvfh xtheadvector infra
* dispatch for rvv and xtheadvector
* dispatch for non-vector zfh
* port xtheadvector recp rsqrt trunc
* general rvv gemm
* c906 and c910 ci
* old tuple code clean
* update riscv64 ci
* update build doc
* drop old th1520 toolchain

* complete abs, fmod and sin function in simplemath.h

* remove some unused variables in simplemath.cpp

* modify test-coverage.yml and add some functions to simplemath.cpp

* modify erf.cpp which included math.h

* include platform.h for NCNN_SIMPLEMATH definition

* move utility constants and functions in simplemath.h to simplemath.cpp

* guard simplemath functions with extern "C"

* add NCNN_EXPORT macro in simplemath.h

* include plateform.h and guard all declarations with NCNN_SIMPLEMATH

* clean unused code in test_unaryop.cpp

* guard #include <vector> with NCNN_SIMPLEMATH in benchncnn.cpp

* add 'static' to guard functions that not declarated in header file

* modify sin and cos with better implementation

---------

Co-authored-by: HonestDeng <HonestDeng@users.noreply.github.com>

* RVV: use size_t for vl

* RVV: replace vsseg.v tuple type by using regex

-----

search:
vsseg([1-9])e(8|16|32)_v_(f|i|u)\2m(1|2|4|8)x\1\(([ -~]+), vcreate_\3\2m\4x\1\(([ -~]+)\), vl\);

substitute by:
vsseg$1e$2_v_$3$2m$4($5, $6, vl);

* RVV: replace vssseg.v tuple types by using regex

---

search:
vssseg([1-9])e(8|16|32)_v_f\2m1x\1\(([ -~]+), vcreate_f\2m1x\1\(([ -~]+)\), vl\);

substitute by:
vssseg$1e$2_v_f$2m1($3, $4, vl);

* RVV: replace vlseg.v tuple types in load/store

* RVV: replace vloxseg2ei32.v tuple types

* RVV: add a wrapper for old compilers

* RVV: add segment load/store wrapper in pakcing

* RVV: fix cmake test

* RVV: make clang happy by dropping VLAs in sgemm

* RVV: add clang cmake toolchain configure

* RVV: add clang ci, riscv64-unknown-linux-gnu

Co-authored-by: thelastlin <thelastlin@users.noreply.github.com>
Co-authored-by: nihui <shuizhuyuanluo@126.com>

* riscv convolution dot function

* move rvv ci to centos

* apply code-format changes

* fix gcov path

* move newlib riscv ci to centos