Use no-inline version rb_current_ec on ppc64le

This commit fixes the failures in bootstraptest/test_ractor.rb reported on
the issue ticket <https://bugs.ruby-lang.org/issues/21534>.

TLS (Thread-Local Storage) may not be accessed across .so on ppc64le too.
I am not sure about that.  The comment "// TLS can not be accessed across
.so on ..." in this commit comes from the following commit.

ruby@319afed#diff-408391c43b2372cfe1fefb3e1c2531df0184ed711f46d229b08964ec9e8fa8c7R118
> // on Darwin, TLS can not be accessed across .so`

This failures only happened when configuring with cppflags=-DRUBY_DEBUG and -O3
on ppc64le.

The reproducing steps were below.

```
$ ./autogen.sh

$ ./configure -C --disable-install-doc cppflags=-DRUBY_DEBUG

$ make -j4

$ make btest BTESTS=bootstraptest/test_ractor.rb
...
FAIL 2/147 tests failed
make: *** [uncommon.mk:913: yes-btest] Error 1
```

The steps with a reproducing script based on the `bootstraptest/test_ractor.rb`
were below.

```
$ cat test_ractor_1.rb
counts = []
counts << Ractor.count
p counts.inspect

ractors = (1..2).map { Ractor.new { Ractor.receive } }
counts << Ractor.count
p counts.inspect

ractors[0].send('End 0').join
sleep 0.1 until ractors[0].inspect =~ /terminated/
counts << Ractor.count
p counts.inspect

ractors[1].send('End 1').join
sleep 0.1 until ractors[1].inspect =~ /terminated/
counts << Ractor.count
p counts.inspect

$ make run TESTRUN_SCRIPT=test_ractor_1.rb
...
vm_core.h:2017: Assertion Failed: rb_current_execution_context:ec == rb_current_ec_noinline()
...
```

The assertion failure happened at the following line.

https://github.com/ruby/ruby/blob/f3206cc79bec2fd852e81ec56de59f0a67ab32b7/vm_core.h#L2017

This fix is similar with the following commit for the arm64.

ruby@f7059af

Fixes [Bug #21534]

Author: junaruga

.github/workflows/ubuntu-ibm.yml

@@ -104,14 +104,8 @@ jobs:
       - name: Run configure
         env:
           configure: ${{ matrix.configure }}
-        # Don't set cppflags=-DRUBY_DEBUG on ppc64le, due to some Ractor tests
-        # failing in the case.
-        # https://bugs.ruby-lang.org/issues/21534
-        run: |
-          if [ "$(uname -m)" != "ppc64le" ]; then
-            configure="${configure:-cppflags=-DRUBY_DEBUG}"
-          fi
-          ../src/configure -C --disable-install-doc ${configure}
+        run: >-
+          ../src/configure -C --disable-install-doc ${configure:-cppflags=-DRUBY_DEBUG}
 
       - run: make
 

thread_pthread.h

@@ -133,8 +133,8 @@ struct rb_thread_sched {
 #ifdef RB_THREAD_LOCAL_SPECIFIER
   NOINLINE(void rb_current_ec_set(struct rb_execution_context_struct *));
 
-  # if defined(__arm64__) || defined(__aarch64__)
-    // on Arm64, TLS can not be accessed across .so
+  # if defined(__arm64__) || defined(__aarch64__) || defined(__powerpc64__)
+    // TLS can not be accessed across .so on arm64 and perhaps ppc64le too.
     NOINLINE(struct rb_execution_context_struct *rb_current_ec(void));
   # else
     RUBY_EXTERN RB_THREAD_LOCAL_SPECIFIER struct rb_execution_context_struct *ruby_current_ec;

vm.c

@@ -594,7 +594,7 @@ rb_current_ec_set(rb_execution_context_t *ec)
 }
 
 
-#if defined(__arm64__) || defined(__aarch64__)
+#if defined(__arm64__) || defined(__aarch64__) || defined(__powerpc64__)
 rb_execution_context_t *
 rb_current_ec(void)
 {

vm_core.h

@@ -2001,7 +2001,7 @@ static inline rb_execution_context_t *
 rb_current_execution_context(bool expect_ec)
 {
 #ifdef RB_THREAD_LOCAL_SPECIFIER
-  #if defined(__arm64__) || defined(__aarch64__)
+  #if defined(__arm64__) || defined(__aarch64__) || defined(__powerpc64__)
     rb_execution_context_t * volatile ec = rb_current_ec();
   #else
     rb_execution_context_t * volatile ec = ruby_current_ec;