testsuite: increase timeout of ghc-api tests for wasm32

ghc-api tests for wasm32 are more likely to timeout due to the large
wasm module sizes, especially when testing with wasm native tail
calls, given wasmtime's handling of tail call opcodes are suboptimal
at the moment. It makes sense to increase timeout specifically for
these tests on wasm32. This doesn't affect other targets, and for
wasm32 we don't increase timeout for all tests, so not to risk letting
major performance regressions slip through the testsuite.

testsuite/tests/ghc-api/all.T

+setTestOpts(when(arch('wasm32'), run_timeout_multiplier(2)))
+
 test('ghcApi', normal, compile_and_run, ['-package ghc'])
 test('T6145', js_broken(22352), makefile_test, ['T6145'])
 test('T8639_api', req_rts_linker,

testsuite/tests/ghc-api/downsweep/all.T

+setTestOpts(when(arch('wasm32'), run_timeout_multiplier(2)))
+
 test('PartialDownsweep',
      [ extra_run_opts('"' + config.libdir + '"')
      , ignore_stderr