i#7260: tool.drcacheoff.purestatic bug fix (#7261)

`tool.drcacheoff.purestatic` fails to build due to `libxxhash` missing.
This library is used by `liblz4` in some cases, and must be statically
linked when building the `tool.drcacheoff.purestatic` app, which we
use in some tests.

We update the doc adding `libxxhash-dev` to the list of packages
that need to be installed to build DynamoRIO on Linux.

Note: `tool.drcacheoff.purestatic` is currently only built in x64 Linux
hosts.

Fixes #7260

Author: edeiana

CMakeLists.txt

@@ -1915,6 +1915,10 @@ if (UNIX AND X64)
       mac_add_inc_and_lib(lz4.h liblz4.a)
     endif ()
   endif ()
+  find_library(libxxhash xxhash)
+  if (libxxhash)
+    message(STATUS "Found libxxhash: ${libxxhash}")
+  endif ()
 endif ()
 
 if (BUILD_CLIENTS)

api/docs/building.dox

@@ -45,7 +45,7 @@ To build DynamoRIO on Linux, use the following commands as a guide.  This builds
   ```
   # Install dependencies for Ubuntu 15+.  Adjust this command as appropriate for
   # other distributions (in particular, use "cmake3" for Ubuntu Trusty).
-  $ sudo apt-get install cmake g++ g++-multilib doxygen git zlib1g-dev libunwind-dev libsnappy-dev liblz4-dev
+  $ sudo apt-get install cmake g++ g++-multilib doxygen git zlib1g-dev libunwind-dev libsnappy-dev liblz4-dev libxxhash-dev
   # Get sources and initialize the submodules.
   $ git clone --recurse-submodules -j4 https://github.com/DynamoRIO/dynamorio.git
   # Make a separate build directory.  Building in the source directory is not
@@ -170,7 +170,7 @@ In order to build both 32-bit and 64-bit on the same platform you'll need
 compiler support for targeting both architectures.  Then install these packages:
 
 ```
-sudo apt-get install cmake g++ g++-multilib doxygen zlib1g-dev libunwind-dev libunwind-dev:i386 libsnappy-dev liblz4-dev
+sudo apt-get install cmake g++ g++-multilib doxygen zlib1g-dev libunwind-dev libunwind-dev:i386 libsnappy-dev liblz4-dev libxxhash-dev
 ```
 
 For older distributions, the `ia32-libs` package is needed.

clients/drcachesim/CMakeLists.txt

@@ -568,6 +568,9 @@ macro(add_drmemtrace name type static_DR no_main)
   if (liblz4)
     target_link_libraries(${name} lz4)
   endif ()
+  if (libxxhash)
+    target_link_libraries(${name} xxhash)
+  endif ()
   if (RISCV64)
     target_link_libraries(${name} atomic)
   endif ()