add trap sequences for emscripten

[Milan Hauth]

i need this for the WASM module of my ccitt_g4_tiff
https://github.com/milahu/ccitt_g4_tiff

fix:
pdfium/core/fxcrt/immediate_crash.h:107:2: error: No supported trap sequence!

possible solution:

https://github.com/milahu/pdfium/pull/1

also use abort as the default trap sequence

[Lei Zhang]

Hi,

You are welcome to modify your PDFium fork however you like. If you
want it in upstream PDFium. then you will need to follow the
instructions in CONTRIBUTING.md.

Is anyone else building PDFium with Emscripten and running into this issue?

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[Milan Hauth]

> Is anyone else building PDFium with Emscripten and running into this issue?

there is

https://github.com/paulocoutinhox/pdfium-lib

they compile pdfium for WASM

without patching the trap sequences

but they use the GN build system

https://github.com/paulocoutinhox/pdfium-lib/blob/master/docs/BUILD_WASM.md

https://github.com/paulocoutinhox/pdfium-lib/blob/master/modules/wasm.py

maybe i see this issue

because i dont use the GN build system

i use cmake to build only core/fxcodec/fax/faxmodule.cpp

https://github.com/milahu/ccitt_g4_tiff/blob/main/CMakeLists.txt

what i find surprising is that

core/fxcrt/immediate_crash.h

requires a GCC or MSVC compiler in

#if defined(COMPILER_GCC)

// ...

#elif defined(COMPILER_MSVC)

// ...

#else
#error No supported trap sequence!
#endif  // COMPILER_GCC

core/fxcrt/immediate_crash.h

is included into all cpp files via core/fxcrt/check.h

> If you want it in upstream PDFium

yes

defining trap sequences for all compilers

seems to be an easy fix

the fallback to abort()

could be guarded with a

#pragma message "falling back to abort as trap sequence. you may want to change this for your compiler"

... better than refusing compilation with

#error No supported trap sequence!