doc: update ccache docs

doc/make/ccache.md

@@ -1,45 +0,0 @@
-Using ccache
-============
-
-[ccache](http://ccache.samba.org/manual.html) is available in many
-systems, and can dramatically improve compilation times. In particular
-if we are constantly switching between different branches.
-
-On Ubuntu, we can install ccache by executing
-
-    sudo apt-get install ccache
-
-Using ccache with g++
----------------------
-
-Then, we can create a simple script that invokes ccache with our
-favorite C++ 11 compiler. For example, we can create the script
-`~/bin/ccache-g++` with the following content:
-
-    #!/bin/sh
-    ccache g++ "$@"
-
-Then, we instruct cmake to use `ccache-g++` as our C++ compiler
-
-    cmake -D CMAKE_BUILD_TYPE=Debug -D CMAKE_CXX_COMPILER=~/bin/ccache-g++ ../../src
-
-We usually use Ninja instead of make. Thus, our cmake command
-line is:
-
-    cmake -D CMAKE_BUILD_TYPE=Debug -D CMAKE_CXX_COMPILER=~/bin/ccache-g++ -G Ninja ../../src
-
-Using ccache with clang++
--------------------------
-
-To use ccache with clang++, create the script ``~/bin/ccache-clang++``
-with the following content:
-
-    #!/bin/sh
-    ccache clang++ -Qunused-arguments -fcolor-diagnostics "$@"
-
- - ``-Qunused-arguments`` option is used to suppress "clang: warning:
-   argument unused during compilation:" warning.
- - ``-fcolor-diagnostics`` option is used to enable clang's colored
-   diagnostic messages.
-
-Reference: http://petereisentraut.blogspot.com/2011/05/ccache-and-clang.html

doc/make/index.md

@@ -59,9 +59,7 @@ Pass these along with the `cmake ../../src` command.
 
 * `-D CMAKE_C_COMPILER=`\
   `-D CMAKE_CXX_COMPILER=`\
-  Select the C++ compiler to use. Because of the bootstrapped build (see below),
-  it is highly recommended to use [CCache](ccache.md) to reduce redundant
-  compilations
+  Select the C++ compiler to use.
 
 * `-D CHECK_OLEAN_VERSION=OFF`\
   The `.olean` files are tagged with the Lean version they were produced with.
@@ -69,6 +67,9 @@ Pass these along with the `cmake ../../src` command.
   every `git commit`. Use this option to avoid the version check. The `.olean`
   files can be removed manually by invoking `make/ninja clean-olean`.
 
+Lean will automatically use [CCache](https://ccache.dev/) if available to avoid
+redundant builds, especially after stage 0 has been updated (see below).
+
 Lean Build Pipeline
 -------------------