Adds a GN build file for the double-conversion library.

Change-Id: I0933c2c355dee13afba1fbcf2d97880866c15e5c

Some files in cctest had a 1-line copyright that doesn't list the
license. This copies the project license to those files, preserving the
date.

Summary:
Emscripten is already included, adding wasm32 the same way for when
build with "plain" clang wasm32 (without emscripten)

Test Plan:
make
test/cctest/cctest --list | tr -d '<' | xargs test/cctest/cctest

Reviewers:

Subscribers:

Tasks:

Tags:

* double-conversion: enable for nios2

Nios2 supports double conversion, tested using qemu:

./main || echo "correct"
correct
uname -a
Linux buildroot 4.19.16 #4 Sat Aug 3 14:46:48 CEST 2019 nios2 GNU/Linux

Solves build error

In file included from double-conversion.h:42:0,
                 from number_decimalquantity.cpp:19:
double-conversion-utils.h:119:2: error: #error Target architecture was not detected as supported by Double-Conversion.
 #error Target architecture was not detected as supported by Double-Conversion.

detected by buildroot autobuilders:
http://autobuild.buildroot.net/results/91e/91eaec34708d91f8a05af189243be0b7cabce31b/

Patch sent upstream: https://github.com/unicode-org/icu/pull/725
Bug report: https://unicode-org.atlassian.net/browse/ICU-20751



[Bernd: Fixed path]
Signed-off-by: Bernd Kuhls <bernd.kuhls@t-online.de>
[Added Changelog entry]
Signed-off-by: Peter Seiderer <ps.report@gmx.net>

* double-conversion: enable for xtensa

Signed-off-by: Peter Seiderer <ps.report@gmx.net>
---
Note:

Double-conversion tested with:

        $ cat div.c
double Div_double(double x, double y) { return x / y; }

        $ cat main.c
double Div_double(double x, double y);

int main(int argc, char** argv) {
  double result = Div_double(89255.0, 1e22);
  if (result == 89255e-22) {
    printf("correct result %e\n", result);
    return 1;
  } else {
    printf("wrong result %e\n", result);
    return 0;
  }
}

Tested for xtensa (using qemu_xtensa_lx60_defconfig plus BR2_PACKAGE_HOST_QEMU_LINUX_USER_MODE):

        $ ./host/bin/xtensa-buildroot-linux-uclibc-gcc -c div.c
        $ ./host/bin/xtensa-buildroot-linux-uclibc-gcc -c main.c
        $ ./host/bin/xtensa-buildroot-linux-uclibc-gcc -o main main.o div.o

        $ ./host/bin/qemu-xtensa -L staging main
correct result 8.925500e-18

Really fixes #73.

That file was removed in a previous commit.

Fixes #112

* Char has size 1.
* More const.
* Allow inlining.
* Compact Bignum sizes.
* Consistent naming.

Reported by seanm (github).
Fixes #111.

* Use memset to clear bignum.

* Improve data locality.

* Reduce size of bignum.

Add `StrtodTrimmed` method, exposing a later stage of the conversion pipeline.
Some tools can do the first stage outside of the double-conversion library and would prefer not to pay the cost of doing it again.

Separates the two main classes into separate c and h files.

Fix naming of `case_insensibility` to `case_insensitivity`.

Consistent macro prefix.

When converting `0x` the converter would assert (or access out of
    boundary).
With `0x1.p1234556666FFFFF` the converter would overflow and not yield
the correct exponent.

* minor bug fix: use free() instead of delete[] to free memory allocated by strdup()

* fix for uninitialized variable problem found by valgrind

* disable assertions for 'optimize' build

* removed -g option that was inadvertently added to CCFLAGS

* ignore generated files

64-bit libraries should be installed in /usr/lib64, not in /usr/lib/
Make the destination lib dir configurable.

Commit e13e72e1 removed
include(GNUInstallDirs) and ${CMAKE_INSTALL_LIBDIR} which broke
installing on 64-bit systems.

Signed-off-by: Jason Zaman <jason@perfinion.com>

This fixes compilation on such platforms.

Fixes #91.

Fixes #89.

Support emscripten

Fixes #62

More info about ARC architecture is here: [1] & [2].
We need ARC supported here for many things like:
 - ICU (see [3])
 - Qt5 etc

[1] https://www.synopsys.com/designware-ip/processor-solutions/arc-processors.html
[2] https://en.wikipedia.org/wiki/ARC_(processor)
[3] https://unicode-org.atlassian.net/browse/ICU-20155

Fixes #81

Large hex literals would lose their minus sign.

Fixes #49

Fixes #48.