Docs: Add doc for RISC-V vector intrinsics

Document which version of RISC-V vector intrinsics has implemented in
GCC.

gcc/ChangeLog:

	* doc/extend.texi (Target Builtins): Add RISC-V Vector
	Intrinsics.
	(RISC-V Vector Intrinsics): Document GCC implemented which
	version of RISC-V vector intrinsics and its reference.

(cherry picked from commit 14c1a8df)

gcc/doc/extend.texi

@@ -14688,6 +14688,7 @@ instructions, but allow the compiler to schedule those calls.
 * PowerPC Matrix-Multiply Assist Built-in Functions::
 * PRU Built-in Functions::
 * RISC-V Built-in Functions::
+* RISC-V Vector Intrinsics::
 * RX Built-in Functions::
 * S/390 System z Built-in Functions::
 * SH Built-in Functions::
@@ -21119,6 +21120,14 @@ Xgnuzihintpausestate extension, which redefines the @code{pause} instruction to
 change architectural state.
 @enddefbuiltin
+@node RISC-V Vector Intrinsics
+@subsection RISC-V Vector Intrinsics
+
+GCC supports vector intrinsics as specified in version 0.11 of the RISC-V
+vector intrinsic specification, which is available at the following link:
+@uref{https://github.com/riscv-non-isa/rvv-intrinsic-doc/tree/v0.11.x}.
+All of these functions are declared in the include file @file{riscv_vector.h}.
+
 @node RX Built-in Functions
 @subsection RX Built-in Functions
 GCC supports some of the RX instructions which cannot be expressed in