gmodule: RTLD_GLOBAL is a bug.

Instead of using RTLD_GLOBAL + dlsym(NULL, use RTLD_DEFAULT which
might have half a chance of working in this multithreaded era.

GNOME/glib#19
12 jobs for master in 23 minutes and 27 seconds (queued for 4 seconds)
latest
Status Job ID Name Coverage
  Build
passed #377362
cross-android_api21_arm64

00:02:26

passed #377363
cross-android_api28_arm64

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passed #377364
cross-mingw64

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passed #377360
debian-stable-x86_64

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passed #377359
fedora-x86_64

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passed #377361
G_DISABLE_ASSERT

00:03:52

passed #377365
win32
msys2-mingw32

00:14:16

passed #377366
win32
vs2017-x64

00:09:52

 
  Coverage
passed #377367
coverage

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77.9%
 
  Analysis
passed #377368
scan-build

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  Deploy
passed #377369
pages

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passed pages:deploy

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