BLST's C server already defines and initializes __blst_platform_cap.
Reference that storage from Mach-O assembly instead of declaring an
additional COMMON symbol. GHC 9.14's runtime linker rejects the strong
C definition followed by COMMON as incompatible sizes (0 versus 4)
when loading simplexmq for Template Haskell.

Only symbol linkage changes; CPU detection and cryptographic operations
remain in the existing BLST implementation.

--- a/cbits/blst/build/mach-o/ctq_inverse_mod_384-x86_64.s
+++ b/cbits/blst/build/mach-o/ctq_inverse_mod_384-x86_64.s
@@ -1 +1 @@
-.comm	___blst_platform_cap,4
+.extern	___blst_platform_cap
--- a/cbits/blst/build/mach-o/mulq_mont_256-x86_64.s
+++ b/cbits/blst/build/mach-o/mulq_mont_256-x86_64.s
@@ -1 +1 @@
-.comm	___blst_platform_cap,4
+.extern	___blst_platform_cap
--- a/cbits/blst/build/mach-o/mulq_mont_384-x86_64.s
+++ b/cbits/blst/build/mach-o/mulq_mont_384-x86_64.s
@@ -1 +1 @@
-.comm	___blst_platform_cap,4
+.extern	___blst_platform_cap
--- a/cbits/blst/build/mach-o/sha256-armv8.S
+++ b/cbits/blst/build/mach-o/sha256-armv8.S
@@ -18 +18 @@
-.comm	___blst_platform_cap,4
+.extern	___blst_platform_cap
--- a/cbits/blst/build/mach-o/sha256-portable-x86_64.s
+++ b/cbits/blst/build/mach-o/sha256-portable-x86_64.s
@@ -1 +1 @@
-.comm	___blst_platform_cap,4
+.extern	___blst_platform_cap
--- a/cbits/blst/build/mach-o/sha256-x86_64.s
+++ b/cbits/blst/build/mach-o/sha256-x86_64.s
@@ -1 +1 @@
-.comm	___blst_platform_cap,4
+.extern	___blst_platform_cap