Make CooperativeSaveEnabled() async-signal-safe(r).

The static local variable `enabled` in CooperativeSaveEnabled() is not
initialized until the first call to CooperativeSaveEnabled(), per the
C++14 standard, section 6.7 ("Declaration statement"), paragraph 4. This
initialization is thread-safe as of C++11, but it is *not* required to
be async-signal-safe. Use a namespace-scope variable instead, since this
is guaranteed to be zero-initialized before main() by section 3.6.2
("Initialization of non-local variables").

getenv() is technically not async-signal-safe either, hence the hedging
in the change summary line. However, glibc's implementation of getenv()
appears to be async-signal-safe in the absence of calls to setenv().

PiperOrigin-RevId: 228588617
Change-Id: I669f555d1c91352d55c606970bb237ec888fa7ca

0 files changed, 0 insertions, 0 deletions