RFR: 8231952: ARM32: Wrong assumption in assertion in LIRGenerator::atomic_xchg and LIRGenerator::atomic_add

[christoph.goettschkes at microdoc.com]

Hi,

please review the following changeset. This patch fixes a wrong assumption 
in an assertion of the C1 LIR generator for 32-bit ARM. The assertion 
assumed that atomic operations are only possible for int types on 32-bit 
arm. This is not true, since the LDREXD/STREXB instructions are use by the 
C1 JIT.

This fixes the 3 hotspot tier1 tests mentioned in the issue.

Bug: https://bugs.openjdk.java.net/browse/JDK-8231952
Webrev: https://cr.openjdk.java.net/~bulasevich/8231952/webrev.00/

Thanks,
Christoph