Support portable build without intrinsics

[wargio]

It is impossible to build currently if you want to have a pure-portable build of the C code.
When we build rizin, we need to support TinyCC which does not have immintrin.h nor intrin.h.
This patch removes some dup declarations and defines the default values for the missing intrinsics.

[oconnor663]

Sounds reasonable to me. @sneves let me know what you think.

@wargio how about including something like this to exercise TCC in CI:

diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index d7d754f..fe6d2fc 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -233,3 +233,17 @@ jobs:
     - name: build b3sum
       run: cargo build --target aarch64-apple-darwin
       working-directory: ./b3sum
+
+  build_tinycc:
+    name: build with the Tiny C Compiler
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v1
+    - name: install TCC
+      run: apt-get install -y tcc
+    - name: compile
+      run: >
+        tcc -shared -O3 -o libblake3.so
+          -DBLAKE3_NO_SSE2 -DBLAKE3_NO_SSE41 -DBLAKE3_NO_AVX2 -DBLAKE3_NO_AVX512
+          blake3.c blake3_dispatch.c blake3_portable.c
+      working-directory: ./c

[sneves]

I meant to reply to this at the time and then just forgot. I think the minimal viable patch to solve this is

diff --git a/c/blake3_dispatch.c b/c/blake3_dispatch.c
index b498058..f8f7400 100644
--- a/c/blake3_dispatch.c
+++ b/c/blake3_dispatch.c
@@ -10,7 +10,7 @@
 #elif defined(__GNUC__)
 #include <immintrin.h>
 #else
-#error "Unimplemented!"
+#undef IS_X86 /* Unimplemented */
 #endif
 #endif
 
diff --git a/c/blake3_impl.h b/c/blake3_impl.h
index ba2e91c..ad3940e 100644
--- a/c/blake3_impl.h
+++ b/c/blake3_impl.h
@@ -46,7 +46,6 @@ enum blake3_flags {
 #if defined(_MSC_VER)
 #include <intrin.h>
 #endif
-#include <immintrin.h>
 #endif

[wargio]

@oconnor663 and @sneves i have applied the changes you have suggested.

[oconnor663]

@wargio apologies, the apt-get install command needs sudo. If you know of a way for me to configure things so CI just runs without waiting for me to hit the button, please let me know.

[wargio]

@wargio apologies, the apt-get install command needs sudo. If you know of a way for me to configure things so CI just runs without waiting for me to hit the button, please let me know.

Unfortunately there is no way since this is my first PR to this repo, but since i'm right now online, you can press it again :) and i can fix issues

[oconnor663]

CI is green! @sneves does this still look good to you?

[sneves]

Sure