[Buildroot] issue with timer_create and openblas after update buildroot from 2019_02 to 2021_02

[Arthur Lambert]

I was able to fix the issue by checking the Openblas history commits. But I
don't really understand the issue...

The issue is coming from here:
https://github.com/buildroot/buildroot/commit/6f29cdeee40e556d26b791fabaff84a09e1a2d5d#diff-0995e357753caee10bbc553c2e7aa033d1df05c0c9799916729d4881d7735d26

By default, the multithreading setting is enabled on Openblas. This setting
is really confusing me. For me, I have to enable the multithreading setting
to use Openblas
in a multithreading context (this is my case !). But it is the opposite!
There is this information in the Openblas USAGE file :

>> #### How can I use OpenBLAS in multi-threaded applications?
>>
>> If your application is already multi-threaded, it will conflict with
OpenBLAS
>> multi-threading. Thus, you must set OpenBLAS to use single thread in any
of the
>> following ways:
>>
>> * `export OPENBLAS_NUM_THREADS=1` in the environment variables.
>> * Call `openblas_set_num_threads(1)` in the application on runtime.
>> * Build OpenBLAS single thread version, e.g. `make USE_THREAD=0`

So I have to add this in my defconfig to build Openblas with
singlethread support to fix the problem:

iff --git a/configs/xxxx_defconfig b/configs/dxxxxxx_defconfig
index 4714080d7e..a760627e2c 100644
--- a/configs/xxxxx_defconfig
+++ b/configs/xxxx_defconfig
@@ -45,6 +45,7 @@ BR2_PACKAGE_PAHO_MQTT_C=y
 BR2_PACKAGE_ELFUTILS=y
 BR2_PACKAGE_LIBUNWIND=y
 BR2_PACKAGE_OPENBLAS=y
+# BR2_PACKAGE_OPENBLAS_USE_THREAD is not set
 BR2_PACKAGE_PROTOBUF=y
 BR2_PACKAGE_PROTOBUF_C=y
 BR2_PACKAGE_HAVEGED=y

How this "conflict" can cause an error on the timer_create feature from
uclibc?
Is my change correct?
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