c-blosc package: Add -std=gnu99 flag for gcc (#11959)

When building with GCC, c-blosc requires the -std=gnu99 flag.
Before this patch, the build would only add -std=gnu99 for GCC when
building on specific architectures; this adds -std=gnu99 in all cases
when using GCC.

var/spack/repos/builtin/packages/c-blosc/gcc.patch

@@ -0,0 +1,23 @@
+diff -u c-blosc-1.16.3/CMakeLists.txt c-blosc-1.16.3.mod/CMakeLists.txt
+--- c-blosc-1.16.3/CMakeLists.txt	2019-03-08 21:38:45.000000000 +0900
++++ c-blosc-1.16.3.mod/CMakeLists.txt	2019-07-08 18:47:00.660334280 +0900
+@@ -197,6 +197,10 @@
+   set(CMAKE_MACOSX_RPATH TRUE)
+ endif()
+ 
++if(CMAKE_C_COMPILER_ID STREQUAL GNU)
++    # We need C99 (GNU99 more exactly)
++    SET(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -std=gnu99")
++endif()
+ # Based on the target system's processor and the compiler being used,
+ # set build variables indicating which hardware features can be targeted
+ # by the compiler. Note we DO NOT check which hardware features are supported
+@@ -209,8 +213,6 @@
+    CMAKE_SYSTEM_PROCESSOR STREQUAL amd64 OR
+    CMAKE_SYSTEM_PROCESSOR STREQUAL AMD64)
+     if(CMAKE_C_COMPILER_ID STREQUAL GNU)
+-        # We need C99 (GNU99 more exactly)
+-        SET(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -std=gnu99")
+         set(COMPILER_SUPPORT_SSE2 TRUE)
+         if(CMAKE_C_COMPILER_VERSION VERSION_GREATER 4.7 OR CMAKE_C_COMPILER_VERSION VERSION_EQUAL 4.7)
+             set(COMPILER_SUPPORT_AVX2 TRUE)

var/spack/repos/builtin/packages/c-blosc/package.py

@@ -33,6 +33,7 @@ class CBlosc(CMakePackage):
     depends_on('zstd')
     depends_on('lz4')
 
+    patch('gcc.patch', when="@1.12.1:1.17.0")
     patch('test_forksafe.patch', when='@1.15.0:1.17.0%intel')
 
     def cmake_args(self):