build-time: remove 20% more by PCH'ing C++ stdlib

It seems like someone implemented precompiled headers a long time ago
and then it never got ported to meson or maybe didn't work at all.

This is, however, blessedly easy to simply implement. I went looking for
`#define` that could affect the result of precompiling the headers, and
as far as I can tell we aren't doing any of that, so this should truly
just be free build time savings.

Previous state:
Compilation (551 times):
  Parsing (frontend):         1302.1 s
  Codegen & opts (backend):    956.3 s

New state:
**** Time summary:
Compilation (567 times):
  Parsing (frontend):         1123.0 s
  Codegen & opts (backend):   1078.1 s

I wonder if the "regression" in codegen time is just doing the PCH
operation a few times, because meson does it per-target.

Change-Id: I664366b8069bab4851308b3a7571bea97ac64022

8 files changed, 67 insertions, 0 deletions

diff --git a/src/libcmd/meson.build b/src/libcmd/meson.build
index 4da1b496b..4dc0714c8 100644
--- a/src/libcmd/meson.build
+++ b/src/libcmd/meson.build
@@ -54,6 +54,7 @@ libcmd = library(
     nlohmann_json,
     lix_doc
   ],
+  cpp_pch : ['../pch/precompiled-headers.hh'],
   install : true,
   # FIXME(Qyriad): is this right?
   install_rpath : libdir,
diff --git a/src/libexpr/meson.build b/src/libexpr/meson.build
index fda6fde2c..9a18c7ab3 100644
--- a/src/libexpr/meson.build
+++ b/src/libexpr/meson.build
@@ -145,6 +145,7 @@ libexpr = library(
   include_directories : [
     '../libmain',
   ],
+  cpp_pch : ['../pch/precompiled-headers.hh'],
   install : true,
   # FIXME(Qyriad): is this right?
   install_rpath : libdir,
diff --git a/src/libfetchers/meson.build b/src/libfetchers/meson.build
index dbb85b84c..365bcd4a7 100644
--- a/src/libfetchers/meson.build
+++ b/src/libfetchers/meson.build
@@ -30,6 +30,7 @@ libfetchers = library(
     liblixutil,
     nlohmann_json,
   ],
+  cpp_pch : ['../pch/precompiled-headers.hh'],
   install : true,
   # FIXME(Qyriad): is this right?
   install_rpath : libdir,
diff --git a/src/libmain/meson.build b/src/libmain/meson.build
index b17247a9d..075aa83b2 100644
--- a/src/libmain/meson.build
+++ b/src/libmain/meson.build
@@ -20,6 +20,7 @@ libmain = library(
     liblixutil,
     liblixstore,
   ],
+  cpp_pch : ['../pch/precompiled-headers.hh'],
   install : true,
   # FIXME(Qyriad): is this right?
   install_rpath : libdir,
diff --git a/src/libstore/meson.build b/src/libstore/meson.build
index f776e9621..65ecacc20 100644
--- a/src/libstore/meson.build
+++ b/src/libstore/meson.build
@@ -220,6 +220,7 @@ libstore = library(
     nlohmann_json,
   ],
   cpp_args : cpp_args,
+  cpp_pch : ['../pch/precompiled-headers.hh'],
   install : true,
   # FIXME(Qyriad): is this right?
   install_rpath : libdir,
diff --git a/src/libutil/meson.build b/src/libutil/meson.build
index 96450fbe2..cfdd0e52c 100644
--- a/src/libutil/meson.build
+++ b/src/libutil/meson.build
@@ -129,6 +129,7 @@ libutil = library(
     openssl,
     nlohmann_json,
   ],
+  cpp_pch : ['../pch/precompiled-headers.hh'],
   implicit_include_directories : true,
   install : true,
 )
diff --git a/src/nix/meson.build b/src/nix/meson.build
index e41399b5d..45303641f 100644
--- a/src/nix/meson.build
+++ b/src/nix/meson.build
@@ -89,6 +89,7 @@ nix = executable(
     boehm,
     nlohmann_json,
   ],
+  cpp_pch : ['../pch/precompiled-headers.hh'],
   install : true,
   # FIXME(Qyriad): is this right?
   install_rpath : libdir,
diff --git a/src/pch/precompiled-headers.hh b/src/pch/precompiled-headers.hh
new file mode 100644
index 000000000..f52f1cab8
--- /dev/null
+++ b/src/pch/precompiled-headers.hh
@@ -0,0 +1,60 @@
+#include <algorithm>
+#include <array>
+#include <atomic>
+#include <cassert>
+#include <cctype>
+#include <chrono>
+#include <climits>
+#include <cmath>
+#include <condition_variable>
+#include <cstddef>
+#include <cstdint>
+#include <cstdio>
+#include <cstdlib>
+#include <cstring>
+#include <exception>
+#include <functional>
+#include <future>
+#include <iostream>
+#include <limits>
+#include <list>
+#include <locale>
+#include <map>
+#include <memory>
+#include <mutex>
+#include <numeric>
+#include <optional>
+#include <queue>
+#include <random>
+#include <regex>
+#include <set>
+#include <sstream>
+#include <stack>
+#include <stdexcept>
+#include <string>
+#include <thread>
+#include <unordered_map>
+#include <unordered_set>
+#include <vector>
+
+#include <boost/format.hpp>
+
+#include <dirent.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <grp.h>
+#include <netdb.h>
+#include <pwd.h>
+#include <signal.h>
+#include <sys/resource.h>
+#include <sys/select.h>
+#include <sys/socket.h>
+#include <sys/stat.h>
+#include <sys/time.h>
+#include <sys/types.h>
+#include <sys/utsname.h>
+#include <sys/wait.h>
+#include <termios.h>
+#include <unistd.h>
+
+#include <nlohmann/json.hpp>