[CMake] Please update the documentation for execute_process

[Jeffrey Walton]

> Below is a typical case for us
> (https://github.com/weidai11/cryptopp/blob/master/CMakeLists.txt). If
> it looks pretty shitty, it probably is. That's the best we have been
> able to come up with based on the documentation.

Below is the example code. We don't know whether it should be:

set(SHELL_CMD sh)
set(SHELL_ARGS -c)
set(GREP_CMD egrep)
set(GREP_ARGS -i -c)

execute_process(COMMAND ${SHELL_CMD} ${SHELL_ARGS}
"${CMAKE_CXX_COMPILER} -dumpmachine 2>&1"
COMMAND ${GREP_CMD} ${GREP_ARGS} "amd64"
OUTPUT_VARIABLE CRYPTOPP_AMD64
OUTPUT_STRIP_TRAILING_WHITESPACE)

Or:

COMMAND "${SHELL_CMD}", "${CMAKE_CXX_COMPILER}", "-dumpmachine", "2>&1"

Or:

COMMAND "${SHELL_CMD}" "${CMAKE_CXX_COMPILER}" "-dumpmachine" "2>&1"

Or:

set(SHELL_CMD sh)
set(GREP_CMD egrep)

execute_process(COMMAND ${SHELL_CMD} "-c" "${CMAKE_CXX_COMPILER}
"-dumpmachine" "2>&1"
COMMAND ${GREP_CMD} ${GREP_ARGS} "-i" "-c" "amd64"
OUTPUT_VARIABLE CRYPTOPP_AMD64
OUTPUT_STRIP_TRAILING_WHITESPACE)

And we certainly don't know what to do with "2>&1" because there is no example.

Jeff

**********

set(SHELL_CMD sh -c)
set(GREP_CMD egrep -i -c)

execute_process(COMMAND ${SHELL_CMD} "${CMAKE_CXX_COMPILER} -dumpmachine 2>&1"
COMMAND ${GREP_CMD} "amd64"
OUTPUT_VARIABLE CRYPTOPP_AMD64
OUTPUT_STRIP_TRAILING_WHITESPACE)

execute_process(COMMAND ${SHELL_CMD} "${CMAKE_CXX_COMPILER} -dumpmachine 2>&1"
COMMAND ${GREP_CMD} "x86_64"
OUTPUT_VARIABLE CRYPTOPP_X86_64
OUTPUT_STRIP_TRAILING_WHITESPACE)

execute_process(COMMAND ${SHELL_CMD} "${CMAKE_CXX_COMPILER} -dumpmachine 2>&1"
COMMAND ${GREP_CMD} "i.86"
OUTPUT_VARIABLE CRYPTOPP_I386
OUTPUT_STRIP_TRAILING_WHITESPACE)

# http://github.com/weidai11/cryptopp/issues/466
execute_process(COMMAND ${SHELL_CMD} "${CMAKE_CXX_COMPILER} -dumpmachine 2>&1"
COMMAND ${GREP_CMD} "mingw32"
OUTPUT_VARIABLE CRYPTOPP_MINGW32
OUTPUT_STRIP_TRAILING_WHITESPACE)

# http://github.com/weidai11/cryptopp/issues/466
execute_process(COMMAND ${SHELL_CMD} "${CMAKE_CXX_COMPILER} -dumpmachine 2>&1"
COMMAND ${GREP_CMD} "w64-mingw32"
OUTPUT_VARIABLE CRYPTOPP_MINGW64
OUTPUT_STRIP_TRAILING_WHITESPACE)

execute_process(COMMAND ${SHELL_CMD} "${CMAKE_CXX_COMPILER} -dumpmachine 2>&1"
COMMAND ${GREP_CMD} "x32"
OUTPUT_VARIABLE CRYPTOPP_X32
OUTPUT_STRIP_TRAILING_WHITESPACE)

execute_process(COMMAND ${SHELL_CMD} "${CMAKE_CXX_COMPILER} -dumpmachine 2>&1"
COMMAND ${GREP_CMD} "Aarch32"
OUTPUT_VARIABLE CRYPTOPP_AARCH32
OUTPUT_STRIP_TRAILING_WHITESPACE)

execute_process(COMMAND ${SHELL_CMD} "${CMAKE_CXX_COMPILER} -dumpmachine 2>&1"
COMMAND ${GREP_CMD} "Aarch64"
OUTPUT_VARIABLE CRYPTOPP_AARCH64
OUTPUT_STRIP_TRAILING_WHITESPACE)

# http://stackoverflow.com/q/12515462/608639
execute_process(COMMAND ${SHELL_CMD} "${CMAKE_CXX_COMPILER} -dumpmachine 2>&1"
COMMAND ${GREP_CMD} "\\<ARM\\>"
OUTPUT_VARIABLE CRYPTOPP_ARM
OUTPUT_STRIP_TRAILING_WHITESPACE)

execute_process(COMMAND ${SHELL_CMD} "${CMAKE_CXX_COMPILER} -dumpmachine 2>&1"
COMMAND ${GREP_CMD} "ARMHF"
OUTPUT_VARIABLE CRYPTOPP_ARMHF
OUTPUT_STRIP_TRAILING_WHITESPACE)

execute_process(COMMAND ${SHELL_CMD} "${CMAKE_CXX_COMPILER} -dumpmachine 2>&1"
COMMAND ${GREP_CMD} "ARM7L"
OUTPUT_VARIABLE CRYPTOPP_ARM7L
OUTPUT_STRIP_TRAILING_WHITESPACE)

# Fixup?
if ("${CRYPTOPP_MINGW64}" STREQUAL "1")
unset(CRYPTOPP_MINGW32)
endif()

# MinGW32
if ("${CRYPTOPP_MINGW32}" STREQUAL "1")
set(CRYPTOPP_I386 "1")
endif()
# OpenBSD and MinGW64
if ("${CRYPTOPP_X86_64}" STREQUAL "1" OR "${CRYPTOPP_MINGW64}" STREQUAL "1")
set(CRYPTOPP_AMD64 "1")
endif()
# arm7l is another 32-bit hard float machine. RPI-3 is arm7l on 64-bit hardware
if ("${CRYPTOPP_ARM}" STREQUAL "1" OR "${CRYPTOPP_ARM7L}" STREQUAL "1")
set(CRYPTOPP_ARMHF "1")
endif()