Migrate to using musl libc sscanf to improve performance. Keep the existing JS vfscanf for Emscripten FS compatibility, and add the musl-specific version to be used when called from sscanf and vsscanf.
Skip the sscanf-requiring tests in suites that don't link to musl libc.
Migrate to using musl libc sprintf family to gain compiled asm.js performance. Keep a copy of handwritten vfprintf and fprintf around to be compatible with the Emscripten filesystem IO library. Also migrate frexp which sprintf depends on to musl libc.
Skip sprintf-accessing tests on s_ suites that require linking to libc.
Improve error messages from SAFE_HEAP_ACCESS function.
Fix test_cases to run after previous musl changes.
Migrate snprintf to musl. Move the most common sprintf-related code to libc instead of libcextra to avoid pulling libcextra in on common runs.
Disable testing the x86 triple i386-pc-linux-gnu in asm2.test_cube2hash, that triple is now deprecated.
Fix test test_sscanf to be spec-conformant in the treatment of scanf format specifiers. According to the standard, %255c matches exactly 255 characters, while %255s matches up to 255 characters.
Remove leftover scanf and printf stubs from library.js
Test s_0_0.test_dlfcn_stacks needs ta2.
Update the simd.js

It bases on
https://github.com/johnmccutchan/ecmascript_simd/blob/b5dce3a7039a6d38cb7922f526cdb49a69f01dc5/src/ecmascript_simd.js

API changes:
* Added shiftLeft, shiftRightLogical, shiftRightArithmetic on int32x4.
* Added equals, greaterThan, and lessThan that operate on int32x4.
* Add bit operations (and, or, xor, and not) that operate directly on float32x4.
* Moved constructors into SIMD module.
* Remove use of "new float32x4" and "new uint32x4"
Move float32x4 and int32x4 constructors into SIMD module.
Add ningxin.hu@intel.com into AUTHORS
add test for shell code not optimized in -profiling builds
fix very large doubles; fixes #2392
Merge pull request #2364 from juj/musl_stdio

Musl stdio
1.19.1
Merge branch 'update_simd' of github.com:huningxin/emscripten into incoming

Conflicts:
	AUTHORS
Remove non-existing include paths.