Replace Goals and Why section with Introduction

Rewrite the introduction of the page to state clearly the goals of
LLVM's libc project.

Reviewed By: sivachandra

Differential Revision: https://reviews.llvm.org/D127174

libc/docs/index.rst

@@ -1,6 +1,6 @@
-========================================================
-llvm-libc: An ISO C-conformant Standard Library for LLVM
-========================================================
+===============================================
+llvm-libc: An ISO C-conformant Standard Library
+===============================================
 
 **llvm-libc library is not complete.  If you need a fully functioning libc right
 now, you should continue to use your standard system libc.**
@@ -9,45 +9,26 @@ now, you should continue to use your standard system libc.**
   :depth: 4
   :local:
 
-Goals
-=====
+Introduction
+============
 
-- C17 and upwards conformant.
-- A modular libc with individual pieces implemented in the "as a
-  library" philosophy of the LLVM project.
-- Ability to layer this libc over the system libc if possible and desired
-  for a platform.
-- Provide POSIX extensions on POSIX compliant platforms.
-- Provide system-specific extensions as appropriate. For example,
-  provide the Linux API on Linux.
-- Designed and developed from the start to work with LLVM tooling, fuzz testing
-  and sanitizer-supported testing.
-- Use source based implementations as far possible rather than
-  assembly. Will try to *fix* the compiler rather than use assembly
-  language workarounds.
-- Extensive unit testing and standards conformance testing.
+The libc aspires to a unique place in the software ecosystem.  The goals are:
 
-Why a new C Standard Library?
-=============================
-
-Implementing a libc is no small task and is not be taken lightly. A
-natural question to ask is, "why a new implementation of the C
-standard library?" Some of the major reasons are as follows:
-
-- Rather than being built as a single monolithic codebase, llvm-libc is designed
-  from the beginning to enable picking and choosing pieces.  This allows using
-  it as a minimum overlay for e.g. faster math functions than might be
-  available on the system library.  This is useful where an application may
-  need to access improved CPU support over what's available on the system,
-  or may need guarantees in performance across different installs.
-- Explicit support for building llvm-libc and code with sanitizer compiler
-  options.
+- Fully compliant with current C standards (C17 and upcoming C2x) and POSIX.
+- Easily decomposed and embedded: Supplement or replace system C library
+  functionality easily.  This is useful to get consistent math precision across
+  systems, or updated memory operations for newer microarchitectures.  These
+  pieces will work on Linux, MacOS, Windows, and Fuchsia.
+- The creation of fully static binaries without license implications.
+- Increase whole program optimization opportunities for static binaries through
+  ability to inline math and memory operations.
+- Reduce coding errors by coding in modern C++ through the use of lightweight
+  containers during coding that can be optimized away at runtime.
+- Permit fuzzing and sanitizer instrumentation of user binaries including the
+  libc functions.
+- A complete testsuite that tests both the public interface and internal
+  algorithms.
 - `Fuzzing`__
-- Be useful for research and review.  By avoiding assembly language, using C++
-  iterators, RAII and templates, llvm-libc aims to have clearly
-  readable code and to improve the compiler as needed to ensure that optimal
-  assembly is emitted.
-- Enable fully static compiles.
 
 .. __: https://github.com/llvm/llvm-project/tree/main/libc/fuzzing